I adored 64DS. It was such a fun game to play concurrently with friends and tell each other about secrets and stars and stuff we found funny (especially while playing the minigames). I can tell it's not objectively the best though (the dpad...ow...) and I haven't played enough Mario to answer.
Edit: oh, I didn't realize this was bumped from 2017 and so I can't answer the poll. I'm all for reviving discussions but...
Super Mario Sunshine is one of my favorites, even if I was never able to finish this game (as I stuck
at one point and didn't had a GameCube later to try it again), I had lots of fun and spent also a lot
of time into it.
Super Mario 64 DS was also a game I enjoyed. At first, I wasn't that much interessed in it, until I got
the chance to play and really liked it from that point on.
Super Mario Galaxy is another one I like and also one of favorite games for the Wii. I would say it was
pretty good, however, I would still prefer Sunshine over it a little bit.
Last but not least: Super Mario Odyssey, which I still need to complete. The game is in fact awesome
and I love the places such as New Donk City a lot. I also really like it that Mario can wear various cool
outfits.
Honorable mention: Super Mario 3D Land, which I find quite entertaining back then when I played it.
It's a biased list. I've decided not to count the ports or sequels.
Galaxy I've 100% numerous times, and I've always found it enjoyable.
Sunshine has so much personality, I haven't 100% it, but if I did, I may even put at as the same as Galaxy.
Odyssey I'm conflicted about, they tried and put a lot of effort into this game, but at times, it's just feels too much?
I haven't played enough of 64, but it's very reminiscent to Sunshine in feeling and needs a remaster, I've put it with 3DS World as it feels mostly as an extension of Galaxy.
I missed the opportunity to vote on this unfortunately, but if could it would be Sunshine! Most of these games are great though! I haven't had a chance to play some, unfortunately...that'll change though!
Of all the 3D Mario games, I think Super Mario Sunshine or Super Mario Galaxy is my favorite. It's tough to choose between them because one of them I have a strong fondness for due to nostalgia, etc. while the other is really good because I had a ton of fun with it and I just love the story it has!