Hello everybody!

I don't know neither of those games series, but I love the Deathrace 2000 movie!

Both series seem inspired by the movie, so I would like to now what are the difference between them, wich one you like the most, why etc...

Camageddon Splatpack and Carmageddon 2 are probably the best.
Max Damage is sort of a remaster of the first game but not as fun imo.

As for Megarace, I never really saw the point of it, it plays like a lane changer and relies heavily on cheesy fmv.

Megarace is literally a FMV game with FMV action sequences. Sorry to burst your bubble.