Super Mario Galaxy is my favorite game this gen and my favorite game since Zelda: OoT. I actually did not enjoy SM64. I think the more open world takes away the emphasis of platforming which is what I like Mario games to focus on whether it is a 2D or 3D game. To me Super Mario Land seems like a natural progression from the Galaxy games as it further combines the elements of the 2D and 3D games.
My favorite level in Super Mario Galaxy is the final Bowser level,I think it was a lot of fun by throwing in a little bit of the gameplay from all of the earlier stages in the game into one stage.I also like the level in the fire world where the volcano explodes behind you.