Super Mario 64 is amazing. I think anyone that doubts the importance and impact of that game on all of gaming and all genres is foolish. I have played and beat Super Mario 64 countless times, and have been impressed with the overall quality of that game...and yet, the game is sometimes lacking something. It is lacking something that many 3D games have for me. Replay-ability. Super Mario World has that charm that I can't resist. If it is available to play, I will play it. I can not count how many times I have played and beaten the game 100%. I have almost every secret engraved into my memory. (Though I know of there are some that elude me.) There are only 2 games give me that much excitement over. Legend of Zelda: A Link to the Past and Super Mario World.
So to me I have to vote Super Mario World, because it is a game that even now I still desire and want to play, and would my kids to play and experience.