Consoles
NES: Super Mario Bros. 2 / Mega Man 2 (Tie)
SNES: Super Metroid / Final Fantasy III (6) (Tie)
N64: Super Mario 64 (No real favorite as I didn't get into the system much)
GCUBE: Animal Crossing / Super Smash Bros. Melee (Tie)
WII: Wii Sports (No real favorite. I have tons of Wii titles on my backlog )
WIIU: No real favorite at this time.

Portables
GB: Super Mario Land
GBP: Pokemon Silver (It's the only game I can remember spending a decent amount of time on)
VB: Mario's Tennis or Mario Clash (Not enough time spent with the system to have a favorite)
GBA: Pokemon Pinball: Ruby and Sapphire / Castlevania: Harmony of Dissonance (Tie)
NDS: Animal Crossing: Wild World
3DS: Project X Zone