Double Dash.

Actually, that's the first one I really liked. Before that I preferred Diddy Kong Racing, and even Mickey's Speedway USA, over any Mario Kart.

This!

And it got especially hectic on baby park because unlike their incarnations in later Mario Kart, items could go right through the middle strip, so you could actually hit opponents on the other side of the track.

Double Dash!! It is still my favorite in the series.
Mainly because I think it have the best battle modes of any Mario Kart in Bob-omb blast and shine thief. The fact that they can go on indefinitely make them to me mor chaotic and fun. We always play on family get togethers.

Mario Kart Wii.

MK8 > MKWii > MKDS > MKW > MK7 > MKDD > MK64 > MKSC > SMK

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.

Double Dash!! I have so many fond memories of playing MKDD with my two brothers. We'd always do All-Cup Tour and while playing two on the same kart took some getting used to, it was so overpowered once you knew what you were doing.

Yes! All Cup Tour was the absolute best :)

Got to go with MK64. I dont think I had as much fun with any of the ones that came after (until MK8)

I still have not tried the latest Mario Kart but so far my rankings is something like:

DD > DS > 8 > Wii > 7 > SC > 64 > SNES

Mario Kart DS. Mission Mode was terrific, it had my favourite stages for Battle Mode, some of my favourite tracks ever (Delfino Square, Airship Fortress, Peach Gardens, DK Pass, Waluigi Pinball...), first game to have online and snaking was awesome to learn and execute.