SMB3 all the way. World is fantastic, but 3 is just a timeless classic. The amount of game on that cart is impressive for NES standards.
I used to hate World for some reason as a kid. I guess I thought it was ruining the franchise or something. Boy was I dumb. When I actually played it for the first time I had loads of fun. I love the game now.
But SMB3 is still my favorite between the two (SMB2 being my favorite overall) and I now know which Mario game I really need to hate: SM64.
