When I think kart racing I always think back to Mario Kart 64 on the N64. There have certainly been better kart racing games since then but I can't think of another racing game that consumed more of my time as a kid as that one did.
I've dabbled here and there with other kart racers such as Diddy Kong Racing and Modnation Racers but in my opinion they just never did it for me like Mario Kart did. It could be that the characters do very little for me or that they sometimes lack the same polish as a Nintendo game but I always kinda just avoided them.
Sonic & All-Star Racing Transformed on the other hand does look super fun and I've heard lots of good things so I may have to check that one out.