1. 64
2. Double Dash
3. Wii
All 3 are great, though
64 is just a classic in my eyes, and not just out of nostalgic value. Double Dash added some amazing courses, twists, characters, etc. The Wii one is cool and I love the steering wheel add on, but its just simply the weakest of that trinity.
Haven't played 8 since I don't have a Wii U but I really want to try it out.
I've watched so many YouTube videos of people playing it and it looks phenomenal.