1) NES
2) SNES
3) Mega Drive (Genesis)
4) Game Gear
5) N64
6) GBA
7) Gamecube
I quickly sold the GBA, because of the horrible screen and cause most of the games were SNES ports. So that has to be my least favourite, though I hardly played the SEGA ones, too.
Favourites: The rest :)
Currently playing: NSMB (Wii)