I have lots of favs lol:
Makoto (P3 Protag): He's a silent introverted guy, but he's cool and OP as fuck.
Aigis: Robots are cool, and she's cute.
Koromaru: He's a dog, so you have to like him by default.
Shinjiro: A cold badass on the outside, a cuddly guy on the inside.
Kanji: he's funny
Naoto: Her chemistry with Kanji is pretty funny, also she's cute and smart.
Adachi: Well if you played P4, you already know.
Joker/Ren: He's hot, and he's in Smash, so you have to like him by default too.
Morgana: Has a nice big head, and is cuddly (also annoys you when you're not asleep).
Futaba: A dumb nerd, but she's pretty good at her job, so I like her a lot.