Impossible for me to tell which one was the best.
I have not played the 1st one.
Mario Kart 64 was my 1st mario kart game, and my 1st N64 game. Very fun, but seems now inferior when compared to the later games.
Super circuit was ok. Again, the later games are better.
Double Dash was pretty good. When playing with my friends, we'd always have heated tournaments, or we'd battle with the bombs for hours.
Sadly, I lost my DS game, but it is quite awesome with its online play. Makes me feel good about my game-playing skills when I beat people from Japan
Sure, it's weird to rant about Mario Kart, but then again, this falls in my "special interest." I'm sure you all understand 