Galaxy is the only 3D mario game I liked. And even so, once I finished I never touched it again.

I am currently playing NSMBW and I am sorry but it beats any 3D mario to date! Is a wonderful game in any sense.

So my answer to your question is:3D. I'll chose 2D mario over 3D any time.

This is such a hard question...but I will have to go with Galaxy. Multiplayer will keep me hooked on NSMBWii, but Galaxy was just so amazing and innovative. I was also hoping NSMBWii would be harder than SMB3, and although I haven't beaten the final world, the other levels were just too easy for my taste.

Hard, since I can't choose both I'll say 2d

Easily prefer 2D.  No contest.

Galaxy. But NSMBW isn't far behind.

Galaxy is an amazing game. NSMBWii is a "for so long time waiting" game.

Waiting for another amazing game: Galaxy 2.

Galaxy... I haven't bought NSMB and am not planning to, so put me down for 3D.

NSMBWii. Four player is awesome beyond words.

I played both to full completion and I loved them. However, I felt New Super Mario Brothers Wii didn't do much of anything new, aside from the multiplayer aspect (which obviously was its major new aspect). But looking at it from all other aspects (the single player/design aspect), it didn't do that much new.  If anything, New Super Mario Brothers Wii was a good example of hitting the 'nostalgia' button. A game trying to combine the best of many past games (mostly Mario 1, 3, World and NSMB) into one game. But by itself, I can only see a few interface changes to the overall game such as a few new mini-games, improved graphics/handling, more levels (which I feel were rather repetitive and similar) and so on. In other words, the game overall was pretty much more of the same, which is hard to say for a Mario title as it WAS fun. But it can't really surpass something like Mario 3, World or even Galaxy because those games were completely unique and as such, completely original and fun experiences. In order for a game like New Super Mario Bros Wii to 'wow' you, it has to work 10x harder because it isn't bringing anything new to the table. And it didn't really do that. It was purely fun and that's about it.

So in this instance, I just have to say Mario Galaxy is better simply because it was not only one of the better Mario titles, but comparable to one of the best. I bought the game feeling skeptical after Mario Sunshine and even rather weary (never was a big fan of 3D Mario to begin with). But the game completely blew away my expectations. And re-invented my view of both Mario and platformers.

Galaxy. Nothing against NSMBWii but I've always liked 3D Marios more.