Albel, Fayt, Cliff, Nel, I've never used anyone else and don't care to.
So far, I haven't even been given the chance to play as Mirage.
In my opinion, Adray, Roger, Peppita, Sophia, and Maria are not worthwhile characters.

For Fayt, I continually added +_% atk to a Holy Sword. (least, that's what I think it was called.) It's the only unique weapon in the game and I really like it. Glowy glass blade-thing. It's rather weak by itself, but it's one-of-a-kind as I can tell.