I used everybody in in turn, and I found that they each had specific roles to play. They're all great.
Stocke is Stocke.
Raynie is your single target multi-element Mage, and a damn good one at that, though later on she gets great AoE spells. Gets her magic mover skill WAY too late, but still gives her an edge over other mages. Then again, Stocke has the same move, and cheaper, IIRC.
Marco is the utility guy. He can move single panels in all directions, and sacrifice his turn for someone else once he becomes useless. He does have Spin Slash to rack up combos... but you're better of giving up his turn for someone else. Oh, and healing, but I just use items.
The Shaman early on requires a mover to activate her trap, but then she gets other toys to rack up combos (2nd best) and soon her MAG allows her multi-traps (and even Cross Star) to kill with ease. She can also steal, but I'd rather make Stocke do it.
Rosch is... I dunno. Tank I guess. He's all physical, but another guy outshines him. He does have Grapple to complement Stocke though, and does get plenty of AoE moves.
The Gunner is just great. She gets a spell that HITS EVERYTHING, and with her MAG, she clears encounters easily. Even early on her spells outshine Raynie when enemies don't have Fire/Thunder weaknesses. She even gets Marco's Trans Turn, if for some reason you'd rather not bombard things to oblivion with Magic.
The Big Guy is awesome as well. Best combo attack, mows things down with his obscene attack, plenty of move panels and AoE options.
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My Little Phineas and Ferb: Summer is Magic!
Aww, I lost to SuperNiceDog, Winner of the Rivalry Rumble Guru Contest