Best: Could winning a battle in Super Mario RPG count? If not, then, Super Mario World.
Worst: I think I'll go with Super Mario Bros 2 (U.S.) as well--you beat a mini-boss at the end of almost every level, and there's no celebration!
Honorable mention: If New Super Mario Bros. had Mario do the peace sign and say "Oh yeah! Here we go!" or something half the time, it would win. I love how in Superstar Saga, the Mario Bros. pose with the move that did the finishing blow.
Nintendo games need more V-signs. Yoshi still does it in Super Smash Bros, but I was counting on Ness to do it as one of his taunts in reference to his pose for the magical Photoman. And Mario... I think he has multiple personality disorder.