Not sure if these ones are too niche, but they were my favourite Genesis games.
Zombies Ate My Neighbors
vs.
ToeJam & Earl
Zombies Ate My Neighbors was also on SNES.
As I mentioned, these are my favourite two Sega Genesis games, so it's really tough for me to decide. I think I'd give it to ToeJam & Earl though. Probably the coolest game of all time, on top of it being really fun to play.