Super Mario Bros. All-Stars. I practically grew up on that game.
And also... *points to username* Ain't it obvious? One of my brothers blew my naive child mind before we got the game when he said that Bowser was a good guy in the game.
Other gems were Super Mario World, Yoshi's Island, Legend of Zelda: Link to the Past, Mega Man X, and Goof Troops.
On the other team, Sonic The Hedgehog 3 and Knuckles.