do you mean for road racing? most people have 6 speeds, but for the autos, well that depends on their power levels, most singles require an auto tranny upgrade and most people get that done by boost logic or sp
Most of the road racers are running the almost-bulletproof Getrag 6spd, which can handle a LOT of HP. The only thing they upgrade is the clutch.
Those with auto's are either running an upgrading Toyota tranny (SP, BL, etc) or the bullet proof TH400 trannies. However, if you are interested in upgraded auto trannies, you'll be more successful asking in the drag racing section, since that's what the high stall autos are best at.