HDD vs SSD vs Hybrid

[Zephyr]

So I'm planning on getting a new laptop to replace my current. I've decided on the model and spec, but there's one issue I'm still divided about: Storage. My options are as follows:

1. 500GB hybrid drive (Seagate Momentus XT, SATA-II 7200RPM)
2. 128GB SSD (Crucial RealSSD M4 6Gb/s)
3. 1TB normal HDD

I know if I get the SSD, I'll want more storage space, so I'd need to carry around an external drive.

So, to my questions:
Has anyone had much experience with hybrid drives? what sort of performance compared to an SSD/HDD? I've heard they can be less reliable than normal hard drives, but how significant is this?
The SSD itself is around £40 more than the other options, and factoring in an external drive would end up ~£100 more expensive than the other options. Thoughts on whether or not it's worth it?
Any opinions/reasons on what I should go for would be appreciated.
Thanks in advance.

[TBS]

Is a laptop with two drive bays out of the question? A smaller SSD (e.g. 64Gb) plus a big storage disk is the ideal combination.

If thats not an option then the hybrids do give some decent benefits from what I've read (no first hand experience, sorry) but will never perform as well as a pure SSD - this review gives a pretty good summary.

[Zephyr]

Unfortunately, the two bay laptop from the place I'm getting the laptop from is 17", which is both more expensive and difficult to carry around.
Thanks for the link, it was helpful.
I think I'm going to go for a hybrid drive: splitting things like the steam library looks like quite a lot of hassle