It's hard to choose between Super Mario Galaxy and Super Mario 64 so I just won't haha. They are both incredible games and among my top 10 greatest games ever.

Yes.
Another thing is that Mario64 was more revolutionary back in the day, but as a game, even disregarding the difference in technology, Galaxy is easily better.

Galaxy is better. Mario 64 was more revolutionary, but gathering each level Red Coins and 100 coins was getting really annoying. I enjoyed more Galaxy and I'm replaying it sometimes.

The concept of gravity is really cool also.

heck yes it is.

The exploration of SM64 was the best. And the fact that there seemed to be something secretive around EVERY corner was awesome.

Therefore Super Mario Sunshine was the best.

In my opinion, no, I prefer Mario 64. I like the exploration more, the ability to take crazy shortcuts, and the fun of getting stars in a more non linear way. That's just me though.

I enjoyed SMG better than any other Mario in 3D

I love the direction Galaxy went, with a camera you don't have to tend to as much as SM64. As far as ground-breaking, however, SM64 wins that hands down. And Sunshine... far inferior to both IMO.

The thing is, SM64 felt almost like combining a Mario game with an exploration game. You never had a "hub" level design in Mario before. You never went into the same level over and over again. Everything was always level to level in SMB1 through 3 and SMW. I didn't care much for the fact that there are far less worlds and just more things to do in each one as part of the gameplay as opposed to more independent levels like the old games. But SM64 being the first with this design was forgivable to me. Now with Galaxy they still use this 'go back into the same world multiple times and do slightly different things' to expand the gameplay.

I think they should design future 3D Mario games with level structure like the old ones had; that's what made them Super Mario games, and leave the 3D exploration to Zelda.

Yes, but probably only until 2 comes out.

Yes, I easily think Galaxy is the best one. It expaned on the concepts of Mario 64 and made them bigger and even more complex, but in a way that was even more fun and 'balanced'. And, most importantly, made it so you needed to utilize all aspects of Mario (and Luigis) actions to complete the levels and the game. In other words, it was one of those games that had a near perfect combination of difficulty and utilization of all the gameplay presented. A feat even Mario 64 didn't accomplish. Which is understandable as Mario 64 was one of the first true 3D games.

On a personal note, Mario 64 is still good, but back in the day and still now, I find some of the levels to be annoying or even frustrating, due to the camera or layout of the level itself. There's none of this in Mario Galaxy. Sure, you might die a few times from falling off a cliff or a disappearing ledge in the 'Matter Splatter' galaxy. But after a few tries, you get the hang of it and its not only fun, it challenges you to proceed on to the next level. In Mario 64, you will die many times to the same thing, but for different reasons. Be it the camera, losing your breath from coins or simply timing a series of jumps wrong. Things that were, for the most part, fixed in Mario Galaxy.

Overall, the name of the game is just balance. And Mario Galaxy has it all. You still have tons of exploration, but still tons of action and platforming. At a good balance. Where Mario Sunshine had you at the mercy of a waterpack with NO offensive value and Mario 64 made you rely too much on fighting your way out of things with a experimental camera (which, looking back, was still revolutionary for its time, but still can't win a gold metal for best Mario game ever).