Most common car at track is the Kyosho, which happens to be the one I like the least.
I like NT1 a lot, although parts are on the expensive side...besides I don't like the idea of a new car/parts every year.
Serpent is the one I like to most. I would have bought the latest version, but a new model is coming out. The shop stocks a nice amount of parts for all these. Otherwise I can order via Internet.