I used just about everyone but Kanji in the game, and I'll use him next time instead of Yosuke since I really didn't like how Yosuke progresses (and didn't like the character either). In terms of overall effectiveness, Naoto isn't too bad, mainly due to the game making instant death spells work more often than they did in P3 (unless you had Samsara/Die for Me! with the respective boosts) but I felt like Naoto's persona had some weird skill progression. I wound up abandoning its physical attacks and sticking with the instant death spells, hama/mudo boost, mind charge, and megidolaon.
However, the party I beat the game with was Chie, Yukiko and Teddie. It's kind of redundant to have two healers there, but Yukiko can also be made into a very effective fire mage (which is what I did, stacking fire boost/amp on her and dropping single target heals). Teddie was one I kept just for buffs. I really never found a great 4th party member in P4, but somehow I bet if I'd used Kanji I'd have found him to be awesome. The main thing is between Yukiko and Teddie, I could fully heal my group with one of them (and also with the MC if really necessary, but for the last few fights he was basically on buff/debuff duty) and Teddie also gets matarukaja/marakukaja, so I was able to keep my party in good shape, even if Teddie didn't really contribute a lot of damage to the fights.
Chie is just great though. She was easily my best damage dealer, and also easy to keep alive due to her high HP and no weaknesses when her link is maxed.
I'm still disappointed there was nobody with debuffs. If they'd dropped some of the crappier physical skills on personas that didn't need them to do something like add rakunda/tarunda/sukunda to characters, I would've probably found characters like Yosuke and Naoto more useful. and it's not like Yosuke can't be made into a decent wind mage, but beyond dekaja and masukukaja, that's all he really brings.