If the other two had released in place of 3D World, that is, which has sold 3.39 million units as of January.

Galaxy 3

Hmm, Galaxy 3 I`d go with. 3D World is great, but it has people divided. Some people love it, and some don`t, saying it`s not a true 3D Mario game that is dearly needed. And Mario 64 would likely only appeal to old fans purely on nostalgia. Unless it was a re-imagining, it wouldn`t move much units either. MG3 though people want, and they say MG 1 and 2 are some of the best Mario games to date.

Galaxy 3

Hard to say, but I think Galaxy 3 would win

Mario 64 successor with a big open world Mushroom Kingdom.

I meant a modern sequel in the semi-open-world style of 64, not a remaster/re-imagining of 64.

Galaxy 3. 3D World may be my favorite 3D Mario game of all time, but sadly everyone else pretty much dismissed it. And it would be weird to go back to a 64 successor after Galaxy, so people would have also felt like it was a step back.

I don't understand what "Mario 64 successor" means. Galaxy 3 would be a Mario 64 successor. If you simply mean a new 3D Mario game with an original concept, unlike what Galaxy 3 would be, then I think that would have sold the most.

Hmm, now that changes things... It would be a close match. I think I`ll go with the successor then, but would be close, depending on what the successor looked like.