MKDS would be the best if it didn't include RED SPAHKS. Seriously, racing becomes more of a challenge to power-boost on every occasion and less of FUN GAME. Plus there's the ability to snake which just ruins everything. I want power-boosting GONE from the next Mario Kart. Other than that MKDS is awesome, oh well, good game ruined.
MKDD has strange controls, but once you get used to them I thought it was tons of fun. I just think the special character-based items were handled poorly, I'm glad they're gone now. Other than that it was pretty good.
MK64 was awesome. The tracks were great, but more importantly it just felt good control-wise. MK64 wins.
MKSC for GBA was awesome too, unfortunately I lost my copy. I figured at the time that MKDS would be so awesome I wouldn't need it anymore, but I guess I was wrong, I still want it back. The tracks freaking rocked.
The original's okay, but the worst of the bunch in my opinion.
THE END