That is a hard one. Speed Buggy, The Batmobile, KITT, Turbo Teen (forgot about him), The Mystery Machine and now Speed Racer. I think for sure that both KITT and the Batmobile would stomp out Speed Racer but I am not sure about the Mystery Machine. They have Daphnie (Michelle Gellar) to impress so I think they would risk anything even going against David Hasselhoffs singing.
If I remember correctly KITT can also be use to amplify voices from inside the car. That is where I got the idea of Michael Knight or David Hasselhoff singing with power. I could be wrong, but I could swear KITT could do that.
Now we have a full on battle between the Batmobile, KITT, Speed Buggy, The Mystery Machine, Herbie the love Bug and Speed Racer. I can't think of any other vehicle that could possibly join in this battle. Then again I am sure someone remembers a vehicle that has not been mentioned.