Super Mario World and Super Mario World 2: Yoshi's Island are the best 2D platforming games created.
I have not played a platformer game without as much care or balance than those 2 games. However saying that, I think Super Mario Bros 3 is more classic than Mario World. It was the game that redefined the direction of Mario platformers and really platform games in general. The suits, the world map, scope of feeling like the Koopas have an entire army attacking the Mushroom Kingdom, it was amazing.
Now, I do believe Super Mario World had many of those story elements in the game, but it was more localized and felt like a smaller adventure. So as much as I want a new Mario World, I realize that can be accomplished with a New Super Mario Bros. 3.
Also, I would save the 2.5D Mario game to be Super Mario Bros. 4, which would be completely new power ups (even if they are similar powerup with a different look) and new gameplay elments.