Probably Gamecube but N64 is essentiallyed tied. N64 has my highest experiences, but Gamecube was longer lived and had more variety.
Zelda Master Quest (where I played Majora's mask for the first time) and
Windwaker
Smash Melee
Sonic Adventure 2 Battle ( spent years in the chao garden)
Phantasy Star Online 2 (the first action RPG I became hooked on)
Star Fox Adventures
Double Dash (my first Mario Kart game)
Wii was great but the tech limits felt especially noticable. Switch is obviously a beast in terms of first party software, but aside from BOTW and Odyssey. The magic isn't quite there. I suspect I'm just especially critical now.