My friend has a RSX-S, and I have an ITR. I have driven both, and they are quite different cars.
IMHO, RSX-S cant compare to the R in almost every aspect, well except for its interior quality. But then again, the R was built to be a race car, so u cant expect to find all the luxuries such as leather heated seats, A/C, in-dash 6 disc CD changer the RSX has...

Overall, the R is more fun to drive, better suspension, better handling, faster, lighter, more race car like.
I might be a little biased in my little review since i own an ITR :P , so i guess ur best bet is to go test drive both car and see which one you like the most.



P.S. I think the RSX-S is more like an Integra x Prelude.


Edit: typo