I used to love the GTR's, FOX and FO8. But now they just don't feel the same anymore.
XFG is an awesome little car, I never really gave it a chance before but I really like it now.
But ultimately the best car has to be the LX4. It's just perfectly balanced, sufficient power and the handling kicks arse. I'm by no means fast in it, but it just feels right.
I really can't understand the popularity of the XRT to be honest. Just because its RWD? Personally I'd rather drive just about any of the other RWD cars than that one. It's a POS, handles like crap, has no grip or brakes etc. As far as I can see its only good for the D word.
The FBM is my favorite car for close, wheel-to-wheel battling. The LX6 is my favorite for its absolute driving feel. The balance is fantastic and it just seems to flow beautifully from bend to bend.
First I liked XRG/XRT, but for some reason started to prefer RB4 and FXO more. Never the less: Any road car beats all single-seaters (Even LX-cars. However, I lack the skills to tame LX-6).
Edit: My favorite single-seater is MRT. Don't know why, 'tho.