Mario Kart 8, easily. It runs amazingly smooth and is gorgeous.

Double Dash is a close second, I loved playing 2-player co-op with my friends as a kid.

Right now for me it's a tie between Mario Kart DS and Mario Kart 8. MKDS had way more game modes which made me play it for a long time, like missions. Also it was the last one to have stress-free (no time limit) balloon battle.

Mario Kart 8 does some wrong things, battle sucks harder than it ever did before. But the normal track design is awesome, and it has some of the best courses from DS. Items are more balanced as well.

MK8 doesn't have Birdo and that's a minus. But MKDS didn't have him either so it's a draw.

to nitpick: MKDS runs at a PERFECT 60 fps while MK8 drops one frame in a second. Therefore my vote goes to MKDS (but really the two are the greatest kart racers ever)

DD than 8...

Seeing as Mario Kart 8 is the newest, of course people are gonna vote for it. (Similarly to my Bioshock Infinite VS The Last of Us Thread)

IMO Double dash. Never played 8, but looks bland IMO. I don't like what they did to the battle modes.

MK 8 and MK 64 are tied for best IMO

I'm extremely disappointed in MK8's battle mode. It really is terrible and boring and I can't for my life imagine there were people at Nintendo thinking this was a good idea. MKDS stays the best for me. The tracks are excellent and it had online and missions for the first time. They should bring back missions.

Probably 7. The drifting is a lot better than the other games (Haven't played Super Circut and 8, barely played SNES and DS)

Always double dash. Twice the items, twice the fun. Times where you could actually strategize in managing your items and it wasn't just down to pure luck.

The ones I have played:

Mk64 > MKWii > MKDD > MKSC = MKSNES >>>>>>>>>>>>>>>> MK7
Sadly, MK8 looks like MK7 to me.

I've played and enjoyed all of them. (except Mario Kart 8, which is gonna change soon enough) The series consists of great games only, that's for sure, but if I really had to choose one, I'd probably take Mario Kart 64 or Double Dash, for reasons of nostalgia.