Depends on your preferences. I love Stunt cars because they can do all the jumps, flips, and spins, and have generally good handling as well as boost when you need it (as you know, Speed cars can't boost unless the meter's full).
Right now, I am loving the Gamestop car (NOT the company; just the automobile). It has great handling for me, I'm very comfortable driving with it, and I think it's my best choice right now. I've heard good things about the cars you get as rewards for jumps, smashes, and billboards....so I might go for all of those this weekend.
I've found my Carbon GT Concept to be my most used out of all the cars that I have. It does stunts extremely well considering it's in the speed class. It doesn't really take much (not counting driving through the gas stations) to refill the boost meter. Although, the downside to all the carbon cars is that when they are scratched up, their scratches look Green on the front side, but the green scratches look is never noticable from the back.
I really like my Carbon X12. It's great that it's a stunt car, since those are the only ones I like. It's fast, got a bit of strength, and handles good (except when you go from a stop to full speed, it fishtails).