Very difficult decision, perhaps part of why this original trilogy is so dear to me is because all are basically equal in how good they are in my eyes. It helps that I happen to like the alternate, platforming focus they took with SPM; I can understand why other big fans of the originals may not like it as much. Ultimately I went with SPM > PM > TTYD but it's basically SPM = PM = TTYD for me, putting any of them in last just feels wrong.
Meanwhile the following games I'm basically considering a different series entirely, considering the stark changes they've chosen to stick with. I've seen enough to still feel like The Origami King ought to be called Sticker Star 3, not Paper Mario. That's not to say it'll be another awful game, maybe it'll be great at what it does. But I still haven't seen much of a reason for the Sticker Star series to hold my interest, especially when these days I'd typically rather stick to indie games for a fraction of the price