Long story short, I think that everything Super Mario Bros. 3 did, Super Mario World did a billion times better.When it comes to level design, music, nonlinearity in branching paths, powerups, etc, SMW just feels loads better. (continued)
(continued) Don't get me wrong, I enjoy SMB3 and think it's a good game. But I think the circlejerk classic Mario fans seem to collectively have about SMB3 being the best side-scrolling Mario game is more than a little bit ridiculous.
My personal opinion is that many people who say SMB3 is the best Mario game hasn't even played SMW... I think it has to do with the fact that in the US the NES was more succesful than the SNES. In my country, is the opposite... Most people only knew SMW but not the former Mario games since the NES wasn't officialy sold here until 1993.