Double Dash was my favorite until I played 8 Deluxe. The revamped battle mode, extra characters, better graphics and other things tipped the scales to make 8 Deluxe the best in the series to me. The Wii U version of 8 is great, but certainly had room for improvement.

In this order:
Double Dash
8 Deluxe
Super Cuicuit
DS

The original was the first game I'd purchased for my SNES. Before I got the system, actually. I sold my Gameboy and 13 games for $100 (because I had no concept of money at the time) and bought Street Fighter II and Mario Kart to prepare for the SNES that I KNEW I was getting that Christmas.

I got absolutely nothing, that Christmas.

But, I digress. I've been playing Mario Kart since the beginning and the series has always been at the top of my favorite games list (aside from the disappointment of MK64) but the last time I really really really felt joy from the series was Mario Kart Wii. After that, it kinda felt like I was playing out of habit and not because I was having a great time.

I know MK Wii is a lot of people's least favorite but it was the best game available at the time when I was most in love with the series so...yeah. My vote.

I gotta add: the voter turnout for this one is insane! Currently 471 people! ?

Double Dash by a last-second blue shell against MK8D. MKWii is distant third

Super Mario Kart.. ah the childhood!

Double Dash!! will always have a special place in my heart, but Mario Kart 8 Deluxe is just too good. I can't think of a better racing game.

64!

I feel like I already answered this like a week or two ago. But anyway.

I said that objectively Mario Kart 8 (the original or DX is the same to me) is the best, but I vote Mario Kart 64. One of my favourite games of all time, and high up in my year-end Top 50 (which I guess it's almost time for again). I would admit though that with this game in particular, a big part of it being so well regarded in my eyes is because of the nostalgia for it and the bittersweet memories of good family times now long gone. Though there's still merit in picking it over later games. Mario Kart 64 is balanced a bit more towards skill rather than the luck and item-use factor. Its courses are fun and varies, without too many gimmicks and each have shortcuts, both intended by Nintendo and not, that can only be done if the player is good (instead of just cutting a corner with a mushroom or whatever), and they actually pay off. Plus the battle mode in MK64 is indisputably the best.

BONUS: I just hope that they continue on with what they've been doing, Mario Kart 9 will be a lot of fun if they do. Oh and have a Wario Stadium remake in it finally!

Mario Kart 8 is the best, but having played it to death on Wii U and Switch I'm definitely ready for the next iteration of the series.