Super Mario World is my favourite.

Here is a controversial opinion:
NSMBWii, NSMBU, and NSLU are tied for second place.

The others to me just don't come close.

Mario Bros 3. Where Nintendo really got the hand of giving each level its own gimmick and identity. The amount of variety they squeezed into a game with such limited mechanics is pretty astounding. 

I'm more concerned with the masochist who chose lost levels. NSMB2 wasn't inspired but at least it didn't actively try to punish you for playing it. And coin rush was pretty fun. Although why they decided to make coins the focus of the game and then not give you anything to do with all of the coins you collect is a mystery that I will never solve. 

The best game is obviously Super Mario World, but my personal favorite is New Super Mario Bros 2. While the whole coin collecting gimmick is ultimately pointless, is does add a certain level of charm and uniqueness that makes me like it more than all others.

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.

Super Mario World. There hasn't been a 2D Mario before or since that matches the quality of World. Mario 3 is a close 3rd if we consider Yoshi's Island a 2D Mario. If we don't then yeah Mario 3 is a close second.

It is a toss up between the two legends, Super Mario Bros 3 and Super Mario World.

Super Mario 3 holds more nostalgia for me personally though, so that gets my vote.

Super Mario World!
It's a blast from the past.
In Super Mario World
you've got to move fast.

Mario and Luigi
are doin' what they can.
Yoshi and the Princess
are givin' them a hand.


Super Mario WORLD!

Mario 3 and Mario World are a virtual tie for me.

Former I like more for the worldbuilding, locales, more creative environments, along with the powerups. Though I tend to enjoy Mario World a bit more as a whole.

Toss up between World and 3, however ill give it to 3 since World took alot of inspiration off 3.

I know the classic ones are vastly superior in creativity and overall level design, but the only one I thoroughly enjoyed was New U. I've played and finished 3 and World, but playing them felt more like a chore, probably because they're old games, which is a stupid reason but I'm being sincere. I didn't like them that much.