This will sound strange, but I played Super Paper Mario first. I loved the game and made it about 90% into the game before I had to take a break due to other things in life. My break from it was so long that I felt lost trying to pick it back up from where I left off. However, instead of starting the game over from scratch, I decided to start the series from the beginning. So Paper Mario ended up being the first game that I played through to completion (I actually did it as part of the beat all N64 games in a year challenge). I loved the game so much, I immediately went straight into TTYD. I loved that game as well. Both games are still today my favorites for their respective consoles. At the time, I favored PM over TTYD, but in hindsight, I think that was because I had a little bit of burnout with TTYD since I played them back to back. Looking back on it, I have more positive memories of TTYD. I eventually got around to starting SPM again and finishing it, but I agree that it isn't nearly as good as the first two. Those 3 are the only Paper Mario games that I've played (although I own the rest).
I definitely want to go back and play PM and TTYD again. I think both games could be successful on the Switch. However, if they never get around to remaking them, the good thing is that the "paper" graphic style ages very well. Both games still look great today on their original consoles.