I absolutely loved Paper Mario for the Nintendo 64. It was a unique game at the time of its release, the graphics were exceptional (at the time), and it had a really nice story line with lots of side quests and things to do.
I love Super Mario Sunshine as I remember only having 3 different games to play when I first got my GameCube. Super Mario Sunshine was more of a surprise for me as it came in a case for Mario Party 5 and I was saving that for when family came over. When they finally came, I was amazed that I got the game as I remember enjoying playing it when McDonald's had GameCube kiosks. From there on, I have fully enjoyed my GameCube and always will as it was how I got my start on gaming back in 2006.
Super Mario RPG: Legend of the Seven Stars is definitely on the top three, so is Super Mario Sunshine, but my favorites are defiantly Super Mario Galaxy 1&2, I can't decide!
I'm probably going to be crucified for saying this but I don't like and main series Mario games. The only Mario game that I've actually liked is Super Paper Mario.
Looks like I never replied to this thread despite how old it is.
My favorite all-time Mario game is Super Mario World. Obviously, that's my favorite 2D Mario too. My favorite 3D Mario used to be Super Mario 64 for the longest time, but after playing Super Mario 3D World, that's now my favorite. SM64 is great, but it always felt clearly different being a 3D game. SM3W feels like it captures the 2D spirit but is still 3D. It's hard to explain.
It kinda irks me that they've ported tons of Wii U games to the Switch, but SM3W still hasn't been ported to Switch, so makes me glad I do own a Wii U.
I got to go with Galaxy. Disclaimer: It's the only one I've completed, so I'm super biased. I've played SMB2 (the fake American version), a good bit of Sunshine, and I've seen at least some gameplay from most games, though.
I just like Galaxy because its the perfect combination of linear and non-linear. Games like 64 were always a bit too open for me. I don't mind open games, but I prefer more on-track experiences when it comes to platformers.
Also, Galaxy has my favorite mood in a Mario game-hands down. I much prefer the darker and more relaxed atmosphere over the bright vibes of the other games.