Mario Kart Wii and Mario Kart 64 are tied. I love all Mario Karts, but in terms of my favorites, these 2 are definitely above the rest. MKWII cuz of all the things to do, Wi-Fi, and great music. MK64 cuz of nostalgia, music, and cuz of all the good times I've had with this game and my friends.
I voted for Mario Kart 64, even though Mario Kart Wii has a ton of good features. I just hate how unlucky you get as you reach 1st place in MKWii. Items such as Blue Shell, POW Block and Lightning start hitting you instantly, letting racers with Stars and Mega Mushrooms hit and pass you.