For me, it's between Super Mario Bros 3 and World.

Both are amazing games, but World edges it out for being just a bit more magical and for having the best sounds and music in the entire 2D series..

I haven't played all of them (including SMW) but my picks are either SMB 3 or NSMB..

Probably will go to NSMB because of better save features :p

Super Mario World

Super Mario World for me. I think it has the best level design and gameplay of the series. The cape is a great item when mastered and being able to throw items vertically was great and was used creatively. Plus, the areas and characters are just so imaginitive to me and I love the castles and ghost houses. In my opinion, best 2D Mario for its time.

The Super Mario World blowout is real... but Mario is platformer gold so it's safe to lean towards any of them.

Whoa, SMB3 and World were neck and neck at first, but now the SNES game is pulling ahead something fierce.

Another poll without my choice...for me Super Mario Land for GB is best 2D Mario game.
Because it's too good and pretty different from other 2D Mario games.

My favorite is actually Super Mario Land 2: 6 Golden Coins on the original gb. The different worlds are really creative and every single level has its own original theme so it never feels repetitive. Granted it's a little too easy but it's fun as hell and I always felt like it was a portable smw due to there being an overworld map.

Of these, Super Mario Bros. 3.

In actuality though, it's SNES's Yoshi's Island for sure.

Super Mario Bros. U. Wall jump, creative level design, HD game, nice visuals... Although Super Mario World might be my favourite one. Nostalgia is involved in this.