Favorites:
Bullet - just because I can control it best.
Banshee - loved it in GTA III, love it here.
ZR-350 - looks good, quick, decent handling.
Comet - small, quick, great handling. Awesome overall.
Worst:
Infernus - feels like it is made of paper, even in small collisions.
All planes - I really suck at flying.
Quad - the one mission that this was required in ****** me off.
BF-400 - I get on a bike real quick and expect a PCJ-600, ends up being this crap.