LogFAQs > #962643325

In the context of their original games, I'd say Teddie. He's a really fascinating character from the perspective of how his personality slowly develops based on the dungeons he goes through and those he hangs out with. He starts pretty reserved and just wanting to impress, but as he hangs out with horny teenagers more and goes through a bath house and strip club, he starts learning the wrong lessons on how to interact with others. He's almost entirely shaped through the plot of Persona 4, warts and all, and yet remains an indispensable member of the team. The whole game is a learning experience for him, and while it's a straightforward and on-the-nose arc (which, to be fair, 90% of Persona arcs are), it's a nice slow burn narrative that toys with the idea of a traditional mascot being reflective of what they represent - in this case, the Investigation Team. Koromaru, by contrast, is a good boy who can and will never do anything wrong, and Morgana has his own arc that... actively eats into other characters' development and is ultimately a lot more traditional while getting swallowed up by P5's massive pacing issues.

... but remove Teddie from the context of P4 and he's absolutely insufferable. No character suffers in spin-offs more than Teddie, him losing his purpose and only being left with puns, harassment, and constant fits of whining that he's not in the spotlight enough. It's really obtrusive at best and writing bad enough to want to stop playing at worst. Morgana, meanwhile, just kind of stays at the same spot, not particularly interesting outside of P5 but less of a weight around the game's neck, and Koromaru gets meme'd into being "the best boy always comes out on top does everything right". And that's really fun.

Overall I'd go Koro > Teddie > Morgana, but Teddie > Koro > Morgana for debut appearances.