My opinion will be rather biased considering I haven't fully dived into the options of every character, but here's my rough opinion so far:
I was skeptical at first, but after this playthrough, I'm gonna have to go with Sabin. Pump him with Stamina and a Life Bell and you won't even NEED Terrato. Aurabolt hits absurdly hard, and is especially useful on undead foes. Sabin has offense, defense, free healing AND free MP for the party. Sabin can take on any role effectively from my experience.
Close contendors go to Locke, since he's fast, hits like a truck, and is a literal life saver, Relm, for easy heals and surprisingly consistent Sketch abillity (2700 damage to Atma every turn! o.O) and Gau for his massive utillity, especially with Griffin (Playing 1.8.4)
I also want to give my boy Setzer some love. He is hands down the most effective healer from what I've experienced. Heals for alot, and has MP for days. Even his Slots heal my party a good 700 HP as early as Daryll's Tomb. His defensive options are godlike, making him survive as long as Sabin (if not longer) and his Slot attacks (Solitaire <3) hit for MASSIVE damage. It's especially awesome since even without using pause/slow mo cheats, I can still hit it roughly 95% of the time, and of course, no MP so...
Edgar is the man. I pumped him mostly with Palidor and he does enough damage with Jump to make Sabin jealous. Even after neglecting his tools, I still find Flash pretty useful.
I've recently come to appreciate Cyan alot more this time around. I kept obsessing over the idea of pumping him full of Vigor and sticking him in the front row only to do not so great damamge till later on. I've found that pumping him full of HP/Stamina and throwing out Dragons and Eclipses from the back row was far more rewarding.
Still not a fan of Mog, Gogo, Shadow, and Strago is taking some getting used to (I have high hopes for him)
Umaro is fun to use, but moves too slow for how little damage his regular attacks do (Haste barely helps)
Terra and Celes are great (Especially Terra) but I find them somewhat boring to use, mostly because they can do pretty much anything. I'm a sucker for characters who are lopsided as all hell (Looking at you, Locke)
