Hmm for a majority of the hardest dungeons (Undersea Palace, Black Omen) Crono and Ayla were a must...Spammed Falcon hit all the way through. I usually threw in Frog since he has decent attack and enough healing to keep everyone up and running.
But after maxing out all the characters stats a few points became painfully obvious....Crono is Hax...Luminaire strongest solo, multi hit attack and even with an absurd physical attack (confuse) that combos well with the magic users. Magus, is a total cruch to the party...Dark Matter is out damaged by Luminaire and he has no duel techs....but he does have the bad ass factor...If only he had a Duel Tech with Crono...Lumin Matter or something...that would have been awesome.
When fighting Lavos-Crono, Marle, and Lucca baby all the way. Luminaire, Antipod 3....and when one is healing Ice Sword 2, or Fire Sword 2. Those are simply the strongest attacks by far when all stats are maxed.
Chrono Cross...Serge...and uhh..er...Kid...Can't remember any other character since they were all mostly forgettable..Eh, anyone else I found remotely useful...and since everyone sort of leveled at the same pace..it never really mattered to much..especially since everyone can cast the same spells...ugh..just thinking about these facts makes me sick...Not only are the characters forgettable but since you can equip with all the same healing or attack spells...they were technically bland as well.