It wins by default because it is newer, prettier, and on a home console in a world where people seem to think portable gaming doesn't count, and that Super Circuit is a port, even though it isn't.
To this day, if I had a chance to rate SC, I'd give it higher marks than Double Dash, only because it is tighter in gameplay, and a more enjoyable one-player experience.
However, the thorn in Super Circuit's side is the fact that full-fledged multiplayer means multiple GBAs and copies of the game. For Double Dash, it's a matter of more controllers.
Oh, and Co-Op is ownage and the salvation of the game.
