The main reason to take the BUK is in low level games it will scare the other team well away from it and its for sniping air recon. Once you start to face more skilled players, yea, its pretty much useless as it is so expensive and therefore can be swarmed by cheap helis or shelled if they even want to bother removing it. The Tung can be your all in one AA but doing so is rather risky because of its cost, non existent armour, and missiles that just love to, well, miss. Personally I'd rather run fully vetted OSAs for long range AA supported by STROP 2s, though with the Shilka being buffed with the DLC patch I might have to try using them instead of the STROP.
Chap is rather cheap and can still limit Pact rotary wings to a great degree while being covered by Rolands, Flackpanzers, and/or auto cannons of some form for the same price as a BUK. And it is NATO's only form of long range AA missile for sniping recon, something which shouldn't be discounted.
And I don't like the Kiowa. Yea, four hellfires on a exceptional optics helo is nice, but it costs a ton and the Gazelle is both faster and cheaper so you can actually scout better with it.
Something I forgot to mention is to also get an armoured CV. Avoid the helicopters and the jeeps, get the M577, Sulton, or VAB for NATO and the BRDM CV for Pact. Unarmoured CVs tend to die when a strong wind or a single mortar shell blows in their general direction.