I love The Galaxy games way to much not to vote for them.

Galaxy 1 = Galaxy 2 > 3D World > 64 > Odyssey > 3D Land > Sunshine

I voted 64/sunshine/Odyssey, thought for me they kind of are tied with galaxy for the characteristics described by JWeinCom, they have different mechanics and world structures that make them unique to play, all of them breakthrough in gaming, even Sunshine, though that may be the lowest point, but i still marvel at what they did with that water effects and mechanics and i liked the presence of more tall/vertical worlds.

Since games were (and kinda still are) so damn expensive we really apreciated games were we could roam freely wander and wander and keep discovering things (we called them new discoveries and new tricks, thought they were programming bugs), in that respect just a tiny bit the 64/sunshine/odyssey are a bit higher in my oppinion,i give to Galaxy's that they were more linear but managed to have amazing tight controls and better boss battles.

My only complaint to Mario games is that they are kinda irregular with the direction and tone they choose for the characters and settings ever since the NES, i know that they aren't that heavy story games, but they sometimes should compromise a bit more on establishing certain aspects of the Mario universe, that sometimes hampers the experience for me as with Mario Galaxy 2 that instead of build on top of the great Rosalina history/setting they went with "Mario Galaxy 2 it's just a giant deja-vu of the first game".

To me 3D world is a fairly fun game, probably because it's like 2D Mario.  I've never played 3D Land.  Galaxy 1 and 2 and Sunshine are all decent games, but I probably like Galaxy 1 the most of those 3.  Odyssey is boring.  It lacks challenge.  Mario 64 is strong contender for "Most Disliked Game I've Ever Played".  

The Galaxy duology is better than 64 or Sunshine, but Odyssey is my favorite Mario game. I'll narrowly give it to the Galaxy games.

Galaxy series without any contest, although replaying Galayx on the switch is a litte bit dissapointing. Didn't play land/world, but mario 3d world looks really fun.

I don't see Odyssey in the same camp as Sunshine/N64, it is kind of it's own thing. 64/Sunshine were pretty linear when getting a star, while Odyssey was way more open for exploration.  This is especially true with Sunshine.

Mario 3D World single player is good, couch coop makes 3D World one of the greatest games created.  Loved the couch coop.

If Sunshine was as great as 64 or Odyssey, this would be a very, very close call for me.
I still think I'd give it to Galaxy 1/2 though. There's just something magical about those games, they feel like childhood imagination crystallized into video game form.

For what i rememeber from sunshine yeah i think it was more linear and even then it wasn't as linear as Galaxy, for 64 maybe it was because of the limitations for the time, but a lot of the stars could be gotten out of order or at any time, in fact the first week i played the game i wasn't able to get the star from Bob-Omb king because i kept tosing him out of the mountain, but i got the Giant Chain-chomp one just out of curiosity to see what happened if you ground-pounded the log where its chain was, same thing when i got the first star by collecting 100 coins, i went to see if i could do that in all worlds and get an extra star because the first time it was so out of nowhere.