if I had to pick one of those, I would go with the ITR. It will probably hold its value a little better than the s2k, and would be a little cheaper to mod. I personally wouldn't go with the audi unless you buy a newer s4 with the 4.2L V8. I always hear how the turbo's go out and are a PITA to replace. I also wouldn't go with a STI since everybody has one. As for the RX7, reliability would be an issue as well. They tend to run hotter and they burn a little oil, which is never good for the turbo's (lack of oil or thicker hotter oil= short turbo life)