N64 Hands down, no contest.
Honorable Mention to the PS1 and Sega Genesis
EDIT: Have Owned
SNES
N64
GameCube
Wii
Practically owned a PS1 (it was my cousins)
PS2
PS3
Sega Genesis
(Also, I've never owned one, but I believe the Sega Dreamcast to be *HIGHLY* underrated. It's a shame that Sega went out of the console business, because the Dreamcast was really just a PS2, way, way, way before it's time.)