Can't decide. I loved Super Mario World but also 64. It was fresh, new, different and I spent a lot of time playing it.
I also liked Sunshine a lot but that was more like than love.
So World or 64. Not sure...

not if you count both ds and n64 sales :P.

OT: For me

1. Super Mario 64
2. Super Mario Bros
3. Super Mario Bros 3
4. Super Mario World

I think are classics, the ones below I don't.

5. 3D Land
6. Sunshine
7. Galaxy 2
8. Galaxy
9. New Super Mario Bros Wii

Sad to see that there is no Sunshine love, anyways here is my top 10 (consists of all genres within Mario):
1. Super Mario Sunshine
2. Mario & Luigi: Bowser's Inside Story
3. Super Mario Galaxy 2
4. Super Mario 64
5. Mario Party 5
6. Luigi's Mansion
7. Super Mario World
8. Mario & Luigi: SuperStar Saga
9. Yoshi's Island
10. Super Mario 3D Land

I really want to replay Sunshine .. hopefully will come out in VC along with Windwaker for Wii U :)

My favorite games are the Galaxy series, I just think it is so well done.

I also feel like Super Mario 3D Land gets significantly less love than it deserves. Probably my favorite handheld Mario game in the last many years.

Super Mario Sunshine and this is why.
I'm 19 years old, so obviously I wasn't around when the "originals" were making their mark. Which is why my choice can't be any of the super mario brothers. I did play Mario 64 around launch on my newly purchased N64, and I remember having a lot of fun with it, but I was quite young and never ended up beating it.
Fast forward, I've off and on owned a Wii, but I mainly played Brawl (400+ hours, totally serious) instead of getting into the Super Mario Galaxy series. I have played them, but not enough to warrant my complete opinion.

WITH THAT SAID. Super Mario Sunshine came out at the perfect time. My only console was a gamecube, I had no friends, all I did was go to school and come home to play video games. So when I got SMSS I spent many, many, MANY countless hours exploring the world and enjoying the story/gameplay. Such a unique game, even when comparing to other Mario games there is still nothing like good old Super Mario Sunshine.
:D

I don't think anyone on this site would doubt that :D Just look at the top 50 game lists of many users.

@topic: My favorite is SMW. Quite similar reasons as ps3-sales! has for SMSS actually. Only difference is that a friend of mine had a SNES and we used to play this games for hours upon hours. As 6-yrs olds. I think we never managed to reach even world 7^^ 

I like the game called Mario&Sonic Zombie Killer. Despite of the fact that it is just a browser game, I find it funny and entertaining.