Used to play that, but not for long, and never really liked it that much. Also played GPManagerpro, which was my favourite for a long time, and also Batracer, which is definitely one of the more fun, and varied manager games out there.
However, I’d say that iGPManager is the best. I played it during beta, and for a long while after that, and it was fantastic. Unfortunately, time constraints stop me from playing these days, but with it continuously growing, and lots of updates to the game, I’m sure to go back, because in my opinion, it was the best by far :)