Mario Kart 64 is flawed beyond belief with its horrible rubber banding. At least item induced rubber banding is something the player can understand.
Super Mario Kart is the best Mario Kart.

If I had to rank Karts, I'd probably go...
Super Mario Kart (Great because it's pure)
Mario Kart Super Circuit (Great because it's closest to the above)
Mario Kart Wii (Bikes are a great addition. Has best multiplayer of all of them)
Mario Kart Double Dash (Just a good game)
Mario Kart DS (Flawed because of snaking)
Mario Kart 64 (Terribly flawed because of rubber-banding)