If I had to rate them, I'd rate as follows:
1- SNES (tie)
1- NES (tie)
2- N64
3- Gamecube
I can't choose between the SNES and the NES. Both were a valuable part of my childhood and I'd feel like a bastard if I picked one over the other.
Now the 64 was awesome too don't get me wrong, it's just no SNES or NES. I'm all about Mario 64, Goldeneye, Super Smash Bros, Jet Force Gemini, etc etc etc
The Gamecube is cool too, and it's got some cool as hell games, but it is no way near as cool as the SNES/NES
I feel sorry for kids today growing up with the ps2/xbox/gc because it's a different world now. What the hell is wrong with old school shit such as side scrolling, snes style graphics and music, etc. No matter how good you can make a 3d person look to me, I'd still prefer a sharply ass animated side scroller (mega man!)