I'd go with the 996TT. It's cheaper (good examples in the 50-60's now), easy to mod and fairly comfortable.
The 997 4S will be ~110k and 996 GT2 are around 100k.
Obviously, if you want a track car, GT2 or 3.
997 4S' are pretty, but if you want more power, sound like a bad choice.
I have no idea about the 930TT, but it's a completely different category--I doubt many ppl cross shop these models.

 

5 years from now, the experts are gonna say the 996tt is one of the best cars porsche ever designed.