So what’s your guys’ favorite Mario RPG? Mine is Paper Mario: TTYD.
This is a difficult question, because there are a good handful of top-quality RPG games throughout the Mario series' history, and I've played the better part of all of them.
I could say that Mario RPG is my favorite, considering the history I have with the game, the style of the gameplay and the visuals, the music, the quirky enemy design, and the fact that it was the first Mario game to establish such a vast expanse of genuine worldbuilding that we had never seen before. The game did a lot, and I still come back to it pretty frequently.
But then, Paper Mario on the N64 is a good entry, too. The first RPG entry for Mario on the Nintendo 64, with a cute, 2D visual style against a sprawling 3D overworld, more worldbuilding to go off of, and such an ambitious little title considering the console it was designed for. It introduced a new way to fight with the debut of the partner system, and certainly made the journey more exciting when you never knew just who was going to join the party next. And then, of course,
Thousand Year Door comes along to even further expand upon what was already established from the previous game, and the adventure seems even more expansive than the last, with new partners, new locations, new enemies, and much more. Easily one of the best Gamecube titles on the platform.
And, of course, there is the illustrious Mario & Luigi series, a series with a wonderful art design, charming stories, and lots of lovely music, as is par for the course. The best one of the bunch, for me, is probably either Superstar Saga, or Bowser's Inside Story. Both have a wonderfully creative story to tell, with new and unique gameplay styles that fit both of them nicely. Dream Team has a special place in my heart, too, for all of the added whimsy and quirkiness of having a Luigi Army, which I still find quite funny.
It's a hard call to make. I think, at the end of the day, My personal favorite would probably have to be Super Mario RPG, although, Thousand Year Door comes
very close. I'd say those two were probably tied for the top in my mind.