Fun idea! I haven't owned that many systems but still a tough go:

NES: Super Mario 3
SNES: FFVI (Toughest one of the bunch to only pick one)
N64: Goldeneye
Wii: Xenoblade Chronicles
Sega Genesis: Sonic 2

PS1: I could cheat and say Final Fantasy Chronicles so I can sneak Chrono Trigger on here... that or Xenogears
PS2: Dragon Quest VIII
PS3: Grand Theft Auto IV
PS4: The Witcher III
PSP: Final Fantasy Tactics: War Of The Lions

Take care all.