Hi mate! thats not an easy question to answer!
I don't like to say that one car is the best on the track since I might take another out and just have the better setup or it be more suited to the track etc...
Probably my favourite car was the original bj4x4, for its strength, ease of use, compatible spares with my b4, etc etc.. the arms were weak but if you crashed hard you knew what was broken before it stopped crashing and it was fairly cheap and quick to fix.
Dont get me wrong it wasn't perfect, but it had a good combination of favourable traits which made it nice to live with and race week after week.
To be honest though, I like all the cars Ive reviewed in different ways, either for their handling characteristics or looks or or or..