I like the Supra/RX7 more for their basic platform. You can make any car faster, and you can make any car look better, but it's a lot harder to change things like weight distribution, suspension geometry, room in the wheel wells(my biggest complaint about the FB RX7
), etc.
If you want, you can put a complete body kit on a car, chop off the roof, graft on chunks of other cars even! You still can't change what's underneath though...