Rx7 FTW hehe but to be honest with you, my rotary has had it's up and downs, you never know when the engine is about to go then a rebuild will set you back heaps!, S15 parts are easy to find, my friend John has one and he can snap up parts easily but with the Rx7 sometimes its a mission. Would need regular servicing, can't miss one if your feeling lazy or out of coin because the seals need to be changed and all the other jiffy.
Overall:
Rx7 FD (has to be series 8): Looks is nice and slick, low and feels like a go kart, engine = ticking time bomb.
S15: Exterior is smooth with a nice aggressive front end, parts are easy to find, 4 seater.
if you want to know more about the Rotarys or my experience, send me a PM
xx