1 - TTYD
2 - Super Paper Mario
3 - Paper Mario

I believe we'll see a new one around 2016.

I love Paper Mario and TTYD pretty evenly...
I liked Sticker Star, but nowhere near as much as the first two...
More than anything, I didn't like the lack of leveling up or the game's pacing (the third world is cruelly long)...
I had to force myself to finish Super Paper Mario, but I will give it credit for some cool story elements...

Same here!!!!

I liked sticker star but as an individual game - it was too short - too different and not (if at all) side quests that wanted you to go back to a certain stage!

Only played 2 Paper Mario games:

1.-Paper Mario
2.-Paper Mario: The Thousand-Year Door

Honestly I haven't bothered with the others because of what people say about them going away from their RPG roots.

1. Paper Mario TTYD
2. Paper Mario 64
3. Super Paper Mario ( small difference between 64 and Super though...)

I really want to see Paper Mario U come out in 2015, but sadly it will come out in 2016....