wich one is a better ride,overall

I assume you mean you will be modifying the cars with available parts and don't mean just plain stock.
If just drag racing on a track then get the supra (higher potential top end power with modifications) but for anything else get the rx-7. It will probably need new engine seals if it hasn't been done already but once you have a new one and have ensured that oil, cooling, intercooling, engine managment are properly set up then it shouldn't need another new seal for years. The rx-7 is known to handle better and road race better than the supra in both stock and modifed forms.

thats a tough question.. the RX7 will need constant rebuilds to it high revving engine and the rotarys like killing seals.. the supra is heavier but you can lose weight and if turbo they are easy to play with to get more hp not like the rotary.. i would personally choose a Nissan Silvia/200sx or what ever you guys call them..

'93 mazda rx7