My top 5 thinking quickly about it:
Mega Drive
SNES
Xbox
Gamecube
PS1
Mega Drive was my first console, and my love for Sega over Nintendo will forever stand (FU Mario!). The games on that were incredible, however what probably helped was I could still try out the SNES when I was 10 upwards because @Findmartin had the SNES so we'd alternate games. Funny thing is SNES seemed to have better co-op games to play together until the PS1. The only real huge shift in games for me came with the original Xbox. Xbox Live changed my life and games overnight and if it wasn't for how i grew up with the Mega Drive, I think my Xbox would win hands down. Its probably why I got big into online gaming and multiplayer games way more in general.
@J4MES OX4D I missed the N64, probably because my lack of love for Nintendo. Although, when I was old enough I got a GameCube and it honestly was incredible how unique their games were. I imagine N64 was the same, especially with the likes of Goldeneye? Racing wise, Gran Turismo was just the best although I played TOCA 1 and 2 alongside V-Rally 1, 2 and 3 way more because of the Championship co-op ability they had.