I don't like how Repede's artes link together. It's awkward and slightly uncontrolable.

Eh...I think Estelle is the worst in my party. Girl never heals me when I want her to and never listens when I give her commands. Repede at least throws me items when I'm low on health.

I dunno. Everyone in your party is pretty damn broken, so calling Repede the worst isn't much of an insult to him.

Yuri - Broken overlimit "tension" skills let him rip through EVERYTHING constantly. Arte spam won't giveyou TP problems either with those skills that recover TP for comboing. Oh yeah, he has Glory too. Pretty much lets you spam Savage Wolf Fury too if you're great at comboing.

Estelle - Eternal Support + Force Field = invincibility for the entire party for the rest of the battle. Easy to pull off thanks to overlimit spam. Spell spam isn't half bad either in overlimit. Also due to eternal support, perma sharpness is quite nice.

Karol - ... Okay I'm not actually sure here. He pretty much doesn't die unless you never heal him though... knockdown combos make it easy to fatal strike though.

Rita - BLAH BLAH BLAH TIDAL WAVE/METEOR STORM/High Tier Spell, etc. yeah Rita's broken.

Raven - Overlimit + Stop Flow...

Judith - Air combos = enemy unable to counter if you do it right.

Repede - Gale Dog. It laughs at everything. Item Pro & Quick Item lets you pretty much open the menu and decide whenever you feel like re-healing the team completely again, and having 99 items just makes your team constantly reviving and healing. Without Gale Dog or insane item usage (which screws up your grade), you can still do simple fatal strike combos, especially with how easy it is to infinite with Lightning Dog.

tl;dr - everbody has something broken, being awful is like having a 9/10 compared to a sea of 10/10s.