For single player, I'd have to go with the 64 version--the course were such a dramatic improvement and brought the game to another level. I'm not all about graphics, but I admit, it did make a difference.
For multiplayer, I'd say the original (SNES). With the exception of Goldeneye (and beating Smash Bros), this was probably my most player game with friends. The courses were flat, which made it easier to locate people, and the mighty feather was perfect for narrow escapes.
NOTE: I have yet to play the DS version, but it will be my next purchase without a doubt.