depends on the race and/or terrain at hand..

anywhere from 15-18. i have left my 8ight alone its gear combo is very universal to my liking.

But your going to have to choice what one you like best. and your driving style may come into play when making that choice.

Start off first by playing with some diff locker oil weights to get the power transfer that you want. - however thats also digging your own grave becuase you will be re-oiling them after every outting :|

only reason i say that is so that you start off learning how to tune your already tunable chassis to drive like you want it. With a new engine and chassis tuned to your liking then the "faster" part of things will come right along with that.