Since some people have been asking for an Ork strategy guide, I've taken the liberty of writing one up.
Keep in mind however that this isn't the be-all and end-all. I've tried to keep this as brief as possible because I'm hoping (maybe somewhat blindly) that 1.5 is just around the corner and will hopefully make much of this obselete. This should however be of some help to those Ork players out there struggling in the 1v1 scene at the moment. There's no doubt at the moment that Orks are underpowered in 1.41 (either that or the other four races are overpowered, making Orks underpowered by default) but if you play your cards right, you should be able to be competitive with many opponents.
I'm not going to go into detail about how the ork population and waagh system works or anything like that, I'm going to assume you already know the ins and outs of how the orks as a race play. This guide is for those of you who already know what they are doing when it comes to Orks and want to improve their game. So newbies, look elsewhere.
This guide has been compiled by myself through my own experience and also watching and talking to higher level players such as Slow_Runner, Santiago4ever, DaNDnTCarE, Fash and Meth. Insight I have gained from forumers such as Vertigo, Chris, psychodil and Rob have also been thrown in. So I'd like to think this guide is fairly complete.
Orks have two real opportunities to win games against opponents of roughly equal skill. The first opportunity comes very early in the game, where the Big Mek and Shootas can cause some real problems and force opponents onto the back foot. The second opportunity comes early in tier 2 when Nobz and Wartrukks hit the field. Both periods of time however only have a very limited window in which you can actually gain any advantage and momentum, and, generally speaking, if you can't win at either of these two points in the game, then you probably aren't going to win at all.
General Ork strategies
The Shoota Rush
This used to be very powerful, and still is against an unsuspecting opponent. It constitutes building 2 sluggas (sometimes even only 1 slugga) for capping, a boyz hut, 1 banner, then shoota, BM, shoota, or shoota, shoota, BM and sending the shootas in to start harrassing as soon as they pop out. If executed right you can have your opponent in a world of trouble, but know when to back off. If you think you may be getting the upper hand on the opponent, it may be worth researching the shooty upgrades while you continue to pump out shootas or tech to something better. Keep in mind though that many players have cottoned onto this strategy now and it's become somewhat of a one-trick pony, as it can indeed be fought off by opponents who know what they are doing, especially on a larger map. Use it sparingly.
This is a bit of a variation on the shoota rush. Instead of throwing down that early banner, replace it with a generator. You'll still have 1 shoota squad and your BM to do some harrassing damage with, and if worse comes to worse you can use your sluggas as well. The advantage of doing this is being able to upgrade your LP's earlier than usual and trying to get some kind of economic advantage rolling. The disadvantage is that your chances of outright winning the game in tier 1 slip to almost zero. This strategy works better on some maps than on others.
Double Generator Tech (suggested by Slow_Runner)
The double generator tech should only be used on fairly large maps as it leave you very vulnerable to any kind of early attack. It's exactly as the name suggests, build two generators off the bat and start stockpiling that power so you can upgrade those LP's as soon as possible and really start econ booming. Pick the time and place to do this though, not only does it leave you vulnerable early but also puts you behind in tech, so you need to make the most of it.
A very risky venture, but has the possibility of catching the unwary opponent off-guard. This involves throwing three banners down in quick succession once the boyz hut is up to start building stormboyz, and soon after, the Pile 'o Gunz needs to be built to get those nob leaders on the squads and to research the choppy upgrade. This will leave you very open to attack while doing so, and the reward isn't that great unless you seriously manage to put some hurt on the opponent's economy. Not the build that is most recommended.
This strategy is quite a bit safer than the Stormboy tech, as it gives you just that little bit more time to get your defenses straightened out. This is often used in conjunction with a good shoota and Big Mek harrass. While you have your opponent busy, get those 4 banners and PoG built, but don't forget to get your economy rolling too...it takes a lot of moolah to keep reinforcing those nobz. Get the armour and choppy upgrades as soon as possible as well.
Once the Nobz are on the field you have two options. You can either put an extra banner down to get access to your Mega-Armoured Nobz, or save a little and get your mek shop up. Ultimately you'll eventually want to do both, but which one you choose to do first depends on the game situation and how the battles are flowing.
It's vitally important with the Nob tech strategy though that you keep your opponent under pressure early. If you just sit there and tech to Nobz without doing anything to worry your opponent, I can guarantee you they will be more than ready for you when you decide to attack.
3 Slugga Build (Suggested by Chris)
This is kind of risky and shouldn't be attempted on all maps. Build your 2nd grot squad first, have 1 grot build the boyz hut then the other builds a gen, queue 3 sluggas, get the mek and then attempt to harass as best you can killing builders/cappers/taking down a point etc. While you're harassing you should be able to afford to upgrade 1 or 2 LPs which gives you a nice fall back as long as you've saved your mek teleport. It's very important not to suicide your mek or sluggas because the upgraded LPs wont hold up to anything on their own. Get your pile o' guns up, keep prodding and poking your opponent if possible and queue up those banners until you can get nobz, plus don't forget to build another gen somewhere along the way. Once your nobz come out push and push HARD, get a 2nd one ASAP then lay down another banner and get MANZ but remember upgrades!
Race Specific Ork Strategies
Orks vs Space Marines
To be perfectly blunt, Orks can't compete with Space Marines once the SM player hits tier 2 and the bionics upgrades kick in with the Chaplain and vehicles. So to beat a Space Marine player, you need to hit them hard, and hit them fast. Get those shootas out as fast as possible and try to bring down those scouts and try to put a dent in their economy. If the SM player has his Force Commander out early, try and target him with your shootas while your BM pounds at him. The best time to take the FC out is early in the game. Not only is he expensive to replace, but once the SM hits tier 2 he becomes a monster and you don't want that early investment on their part paying off like that. Use any stray sluggas to tie up any tac squads the SM player might build. If you can somehow get to tier 2 with Nobz and MANZ before the SM player can get his uber tier 2 weapons to the field, you'll go a long way to winning. Just don't fall into the trap of chasing him around all day while his tac squads are all being equipped with plasma and heavy bolters because it'll come back to bite you hard.
The Scout Rush
The scout rush is probably the easiest of the SM strats you can expect from an ork's perspective. Clever placement of your early buildings near your strat points will put a stop to it most of the time. If you see 2-3 reinforced scout squads coming at you, you know the scout rush is on. This build doesn't involve a barracks until very late though, so grot infiltration is vital. Get that researched, build and repair those LP's as fast as possible, get your BM out as well as a good amount of shootas, and then push into the SM's base for the win.
The Assault Marine Mass
Uh oh. If an SM player decides to mass ASM's at you, you're going to have a very difficult time bringing him down. The best strategy is to mass him back with shootas, but remember to keep those sluggas capping points. If you can, try to lure him into the fire of some of your buildings guns to get just that little bit of an advantage. You're going to need to micro your shootas and BM around like crazy while you madly attempt to tech to Nobz before he reaches tier 2 and critical mass of ASM's. If he gets to tier 2 before you do, it's GG. Try and dent his economy if you can whenever the opportunity presents itself. Watch out for the ASM's melta bombs...5 of them will bring down your HQ instantly.
Orks vs Chaos
As soon as your opponent draws Chaos, you are fighting an uphill battle as orks. Chaos are extremely difficult to take down in any tier, but the best bet is definately tier 1 and very early tier 2. Once tier 2 reaches a certain point you are on the downward spiral, and it's nigh impossible to win once Chaos hits tier 3. Don't build too many shootas against a Chaos player...Chaos vs orks will very often come down to a teching race...can orks get to nobz first or can Chaos get to berzerkers first? You are going to need to find a way to slow down the Chao's player's teching enough for you to get those Nobz out, complete with armour and choppy upgrades, and preferably with MANZ along in tow to have any chance of beating a Chaos player. 90% of Chaos players will open with a Raptor harrass. There really isn't anything much to worry about here as Orks, your BM should be more than capable of handling the raptors by himself, just don't forget to LP your points as soon as possible to prevent them decapping you. Chaos players will rarely build more than one squad of raptors against orks, but they are often followed by something much nastier.
Don't worry too much about vehicles against Chaos as a general rule...by the time your vehicles arrive your opponent will probably have a couple of horror squads already queued up in his sacrificial circle just waiting to be teleported onto the battlefield. Let your nobz and MANZ do most of the work and use trukks, traks and Kans as support if you can afford them.
Orks have no answer to Chaos tier 3, so if the game ever reaches that point, it's all over. Massed Predators are also next to impossible for orks to take down.
Aspiring Champion Tech
Oh how I loathe this strategy. It's so easy to do and extremely powerful. This involves the Chaos player building several cultist squads and his Chaos Lord, usually with a squad or two of CSM's along for the ride. The armoury and a power gen are built as soon as the barracks is finished, then power swords and plasma pistols are researched. Aspiring Champions are put in to the cultist and CSM squads, and often grenades and heavy bolters are added. If you see a Chaos player doing this build, you MUST take him down before he reaches critical mass. If the Chaos player has taken this route it means he is delaying his tier 2, so feel free to combine shootas with stormboyz and your BM. Tie them up at much as possible - the less those plasma pistols are firing the better. You are going to need to finely balance your troop production with your tech, because ultimately you'll need those nobz and maybe vehicles to finish the job.
Fast Berserker Tech
This strategy is almost impossible to stop on certain maps, which is completely stupid if you ask me. Anyway, if a Chaos player is doing this, he has completely forgone tier 1 apart from a couple of capping cultist squads and is going STRAIGHT for tier 2. I mean he builds a barracks, power gen and armoury, then kicks off his tier 2 research. Once that's complete the berzerkers arrive, usually with the sorceror in tow and it's usually downhill from there if you are orks. If you see a Chaos player with only a couple of cultist squads, it's a dead giveaway that he's going for the fast berserker tech. The most important thing to target here, I believe, is his barracks. You've got no chance of taking the HQ down that early in the game so there's no way you can interrupt his tech once it's started. There's also no point targetting his economy, it wastes time and he's probably already got enough saved up for his zerks. Hit him hard and you should bring that barracks down before the zerks show up, THEN worry about bringing his econ down. Don't miss the opportunity to take cultists and heretics down as well - he can't rebuild them while his tier 2 tech is in progress.
The other alternative to this is to fast tech yourself, get to nobz as fast as possible and meet him head on. Remember your armour and choppy upgrades - Nobz will lose to zerks without them. I wouldn't recommend taking this option though, as without harrassment, the Chaos player WILL out-tech you.
Orks vs Imperial Guard
I believe Imperial Guard to be Ork's most balanced matchup, although some other players may disagree. However, like SM and Chaos, there comes a point in late tier 2-tier 3 where orks simply cannot win against IG, so again, you need to hit them as hard as you can at the earliest possible time.
The advantage to playing against IG is that you almost always know what to expect. 2, maybe 3 guardsmen squads with Commissars attached and the Command Squad will try to hit you early 99% of the time. Your BM and some shootas should keep them busy for a while...try luring them into your buildings guns for some extra fire support. An upgraded banner or two and an LP2 work wonders here. If you can, target the command squad and get grot infiltration happening...once the CS is down you can repair those firing buildings until the cows come home. However this isn't enough. While all this is going on, you're going to need to get three banners plus your PoG up, and start pumping out Stormboyz, preferably with Nob leaders. Once the IG player starts equipping his guardsmen with grenades, you are in real trouble unless you have stormboyz. Get the armour and choppy upgrades and constantly jump those Stormboyz into the middle of the guardsmen squads, constantly forcing retreats and killing a few. Don't be afraid to retreat yourself if things are starting to look hairy. You'll need to be very patient when fighting IG, don't tackle their base head on until you have the heavier hitting stuff, although don't miss the opportunity to do some damage to their economy. Keep the Stormboyz flowing while you tech to either Tankbustas or vehicles to fight the IG vehicles that are on their way. Only build Nobz if you can afford them, although MANZ aren't a bad idea. If you can get some sufficient AV out before enough IG vehicles show up, you have the game in the bag and you can push for victory. Remember IG don't have much of an answer against Killa Kans so if you have the opportunity to build them don't hesitate.
Again don't let this get to tier 3 or you're a goner.
Whatever you do, don't let an IG player cap a point near your base early in the game. Once that LP goes up it'll normally be followed by an infantry command or tactica control and there's no way you'll penetrate that in tier 1 and it'll be all downhill from there.
Orks vs Eldar
Eldar is probably Ork's most difficult matchup. Fleet of Foot Reapers will mince sluggas and shootas, as will banshees. The Farseer will also cause you a world of hurt, especially in tier 1. You need to make as much use out of your BM as possible, Try tying up those reapers with sluggas so they aren't firing very much. Try constantly being on the move away from banshees while your shootas and building guns are spraying fire everywhere. One way or the other, you are going to need to seriously outplay an Eldar opponent right from the word go to beat them as Orks.
The Farseer is a big problem for orks in tier 1. Her spells can turn the game in an instant. If you can, try and knock her out if you get the opportunity, don't let her get away if you have her right down in the red. She's expensive to replace in tier 1 and the longer she stays alive the more likely Eldar are going to win.
Because of Fleet of Foot, Eldar are probably the hardest of the races to hit early and do any real damage to. However, you are going to need to do as much damage as you can in tier 1 because once Eldar reaches tier 2, and vehicles, Warp Spiders and Fire Dragons enter the battlefield, you're in real trouble. When you hit them, target their power. Eldar tech is very heavy on power and if you can slow that down somewhat, you've got a good chance of beating them to tier 2 and getting enough troops out to tackle the heavy hitting guys Eldar can bring forward. Once enough Warp Spiders and Wraithlords are around there isn't much you can do to stop the Juggernaut, so you've got to take them out before it reaches that point.
2-3 Wraithlords with Brightlance upgrades, or a couple of squads of Fire Dragons will level an Ork base ridiculously fast, so watch out for Eldar players that exploit this. Sluggas or Stormboyz are perfect for tying up FD's with while they are blasted by the building guns, although for Wraithlords you'll definately need some AV around. You can breathe a little easy that you'll almost never see Fire Prisms in a 1v1, as Eldar's tier 3 is just as bad as Ork's is. Eldar certainly don't need FP's to beat Orks though.
An Eldar that uses a conventional build (2-3 guardians, farseer, either reapers or banshees early) is extremely tough for Orks to beat. Ironically, it's when the Eldar strays from the norm that things swing in favour of the orks somewhat.
Fast Vehicle Tech
I love it when Eldar goes for fast vehicles, it's the best chance I have at beating them. If you see only 1 or 2 guardian squads running around, with no farseer on a map with a thermal point, it's a pretty safe bet that the eldar is going for fast vehicles. As soon as you realise this, try and slow down the production of that soul shrine while you madly tech to tankbustas. The TB's should easily handle any Falcons that pop out, and you are going to need to take down any source of power the Eldar has and fast. Warp Spiders will normally follow the vehicles, but by then, your nobz should be well on their way and should take care of the WS before they do any real damage. Take down the support portal and the whole strategy has fallen flat on it's face.
Orks vs Orks
This is actually quite a difficult matchup. It's a guessing game of sorts...will my opponent tech to vehicles? Nobz? MANZ? Will he try out-massing me?
What you do against another ork player depends on the game situation. One of the best options is to fast tech to Wartraks and then drive them into the opponent's base to take their banners down. Another option is to try and get more nobz than your opponent does faster. You may even want to think about going for tier 3 as the Warboss and docs can swing the tide of battle in your favour. MANZ are almost mandatory against other orks as they are almost impervious to building guns. Armour upgrades, choppy upgrades, dakka upgrades, upgrade anything you can to give you just that little bit more of an edge in battle. Remember he's got exactly what you have. Whatever you do, don't waste a lot of resources on tier 1 troops, those building guns hurt and shootas are a waste of resources if you can't do any real damage with them.
Just remember it's not always the best idea to tech. While teching to vehicles is a good idea, remember TB's are quite good at bringing ork vehicles down and if your opponent has enough of them that will be a lot of money wasted on your part.
Hope that helps!
If any other Orky players want to add to this, feel free to post underneath