Super Mario 3 by a mile. If platformers were my favorite genre, then I would say it's the best game ever made. It's definitely the best platformer ever made. They packed so much game into that game. It feels like there are secrets to find everywhere. My #2 would be NSMB Wii because of the 4-player. After that would probably be Mario 2 (USA). Mario World was definitely a fun game too, but also a little disappointing. They made it too easy. Yoshi was a cool addition though. Also I might put Super Mario 35 somewhere into my top 3, because that is also a great game, but might not be around much longer.
Bonus: Mostly I want a 2D Mario game with the same basic mechanics, some new types of power ups, but especially a bunch of new types of worlds. Maybe Mario has to invade Bowser's Kingdom or something and then there are 8 worlds there to explore. Or maybe it's some completely new type of world. The truth is that the last few 3D Mario games have had lots of great world ideas. I want to see this level of creativity applied to 2D Mario.