Naoto + Mahamaon/Mamudoon + Megidoloan w/Mind Charge= 10 second battles in the late game
or
Yosuke Strike's silly animation and stats that don't go higher than mid/upper 60s
I'm gonna have to go with Naoto. She gets Garudyne (which is the only reason to have Yosuke in battles) and Heat Riser and her offensive stats are better (STR, MAG, and AGI) and improve with the weapon you find in her dungeon's boss room (gives +5 to all stats). Plus, her weapon is a gun.
Yosuke can come in on his scooter to help out sometimes, too, but he's only good in the early game.
Yeah, her voice is bad, but her positives outweigh this.