It might be Rock Band. At least there's some sort of variety.
Mario's a good choice too because it's so expansive, and again, the variety. That's assuming the sports games (golf, tennis, kart) and the Mario Party games are included.
Mega Man is the classic sentimental pick for me, but I feel like they'd get stale, plus a big chunk of the classic/X series are sub-par.
I'd consider Halo if I had Xbox Live. That'd also be a big factor in Rock Band.
I just never got into Zelda games. I didn't really care for the style of game when it was on the NES, SNES, or Game Boy. The N64 games were cool, but I got rid of both my GameCube and Wii before the Zelda games for those systems came out.
Never played a Final Fantasy game.