Definitely Mario Sunshine. That game is so fun. I love seeing how high you can climb in a stage with Fludd and wall jumps. The Mario Galaxy games made me motion sick sometimes with the weird gravity.
I think it's hard to compare these. Mario 64 and Sunshine are in one category, while the Super Mario Galaxy games and Odyssey are in another category. I like to define the categories by whether or not there is a "home base" so to speak. It really changes the atmosphere of the game.
Mario 64 is so iconic. And the game was so revolutionary at the time. In my opinion it still holds up pretty decently to this day. It's fun, challenging, and nostalgic. Definitely my favorite.
Super Mario 64. The game looks like crap but it still plays beautifully. Still as smooth and fun as always. The only one that compares is Super Mario Odyssey.
Going with Sunshine although I like them all (haven't played Galaxy 1 though). Great music, atmosphere, and the controls are not so clunky like in SM64. 64 was the first game I ever stayed up all night playing though haha so it has some pretty big nostalgia points.. but Sunshine is just so fun and colorful *-*