Mario Kart 64, Mario Kart DS and Mario Kart 7 are all really close for me. Mario Kart 64 perfected the formula in many ways, it set the standard for future entries. I also like that there are distinct differences between the characters rather than vehicles, wheels etc. Mario Kart DS wins on content, while Mario Kart 7 has some of the best tracks in the series. At the end I voted for 64.
I hate Mario Kart Wii, it is so terribly balanced, it is obvious that including 12 racers was a last minute decision, the game is just not designed for it. I think it somehow also controls worse than the other games in the series, and the drifting is much much worse. It is not unlikely to get hit by 3-4 blue shells in a single race and in Mario Kart Wii it stops you completely for several seconds, it is not fun, just frustrating.
Double Dash, SMK and SC I have not played enough to judge.







