I am pleasantly surprised by your list, Sworddude. It is actually similar to how I would do it with a few differences. I was certain most people where gonna do the bog standard MK8 as the top every time.
S: Double Dash
A: Mario Kart Wii, Mario Kart DS
B: Mario Kart 8
C: Super Mario Kart, Mario Kart 7, Super Circuit
D: Mario Kart 64
Double Dash is my all time favorite. I love the tracks, I love the doubles system, I love the controls.
Wii and DS are next on how much I've played them and also great in most regards. I wish snaking didn't exist in DS, but you get used to it. DS also had all those amazing mission modes, and I do really like Wii's cycles and tracks.
Mario Kart 8 is where things go down... I can't justify putting it lower because it has SO much content, but this is in the coin system being brought era... and I HATE the coin system. Mario Kart improved so much when it was removed, but now it seems like it may be back for good... god, I hope not.
Super Mario Kart is really nostalgic and it's battle system is second best, but too many improvements have been made. MK7 is a worse version of MK8. Super Circuit is in the same realm as SMK, but I have less nostalgia for it.
Mario Kart 64 is the most boring and standard of all the games in my opinion. I don't think it improved on SMK enough and I think the tracks go from boring to even poorly designed. It's ace, though, is that it has the best battle mode in the franchise. Much like reintroducing coins was bad to me, ditching the battle system of the first 2 games in most of the series is a baffling decision to me.