Without a doubt it is ToeJam & Earl for me, I banked in so many hours into it, trying to get from world to world, and the multiplayer was great. I remember playing for hours upon hours with my friends, trying to make it from world to world, chucking tomatoes and dodging attacking mailboxes, Mad Scientists, and many other odd humans.
The music still today is the most memorable music from almost any game I have played, even though it was a loop, it reeks of the early 90's and to this day keeps its same feel from when I was a kid.
Definitely a A+ title for me, wish they would do a re-release.