Super Mario World with SMB3 in a close second.

Super Mario Bros 3 and Super Mario World.

New Super Mario Bros Wii.

Couch coop FTW!

Super Mario World and Super Mario Bros. U

Super Mario World, obviously! :P

Level&world desing is the best.
Enemies and bosses. Though some bosses are not that exciting, they are always different. I loved the rhinos and the boo boss, and it has one (if not the best) of my favourite Bowser´s fight from the whole series.
Secret paths/hidden levels. Bonus world was amazing. Exploring the map was like an adventure, it didn´t feel like a map, it felt like you were actually exploring.
Visuals and music.
God, that game was something!

Super Mario Bros 3 imo.

It's a toss up between World and 3. I can't decide.

Dang, I was going to say Mario Bros 3, but then you put Mario Maker in there too. The perfection of 3, or an endless amount of stages, some of them being really clever and brilliantly designed stages? That is a hard call for me to make...

For the first few hours, you were absolutely right, but after that World pulled ahead, and at this point I think it's safe to say it has won the poll.

Mario World because it has the best controls and best level design of all the 2D games. It only disappoints slightly in the power up department, but it kinda makes up with the Feather!