They are all great games. Of course you can't go wrong with any of them.
Mario 64 is a classic. It has tremendous replayability and amazing visuals.
Paper Mario...awesome RPG, especially with all the current hype around Super Paper Mario and the talk that this is the "lost treasure original." Unfortunately, it has no replay value IMO.
OoT is great fun. Puzzles, sword fighting, long ass gameplay, great dialogue and storyline...awesome.