My ranking is
1. Super Paper Mario (i love everything about its story and characters, I eat that angst and melodrama up, I love the distinct geometrical look of the other dimensions and their characters, and the gameplay is fine. This game has the most exaggerated and forced hatebase I've ever seen)
2. TTYD (Best gameplay in the series, overall probably the best blueprint for stories & character design too, it's just immaculate. I want these characters to come back and be recurring, like more than just the ones that currently have appeared across the first 3 games)
3. PM64 (basically what I said about TTYD, this one's just lower because I think TTYD improved and refined most of the elements I value the most. Still, this is how character design should still be in the series)
(first and largest gap)
4. Origami King (lots of great ideas, you could tell they really wanted to get OG fans back on board after the criticisms for the previous two entries, but sadly the freedom to actually do so was still not there yet. The interviews for this game, and what they say about how their hand was still forced to avoid OG style character design, depress me to no end)
(second gap)
5. Color Splash (Sticker Star if it at least tried, but that's really not saying much. The story is at least less bog-standard, but you can only do so much when limited to pre-existing characters, so it still left way too much to be desired. Certain gameplay mechanics were also actually made worse than they were in Sticker Star. This game also had frustrating interviews illustrating just how strong the internal push was to avoid what makes Paper Mario great)
6. Sticker Star (how you can go from Super Paper Mario to this is something that should be scientifically studied. Like this game almost feels hand-crafted to be exactly the opposite of why I love the earlier games, and the fact that its influence stuck around for 2 more games like a stench only makes me resent it more. The interviews for how this game progressed through development genuinely make me angry, as the earliest prototypes looked promising)