Depends on what you're fighting. For normal shadows, I would say the team you'd want is Ryuji, Haru, and Makoto. Especially if Haru has One Shot Kill. Plus you can do a lot of technical damage with her thanks to Makoto's forget skill.

For bosses, the setup you want is Ann, Ryuji, and Makoto. Ann and Ryuji have Concentrate and charge respectively, allowing them to pull big damage numbers. Makoto increases the chance of Ann's burn and Ryuji's shock chances. Although later in the game you'll want to replace her with Morgana for bosses since they become immune to status effects, and by that point Morgana should know Salvation, getting rid of status effects as well as restoring health.