I'm going to crack down on the cast of FFVI, just because I think fourteen playable characters is a bit over the limit for usefulness, which is how I will judge this.

Terra: No problem here. Well rounded magic/physic user? Ok. And then the Transform tech? Now I'm interested.
Locke: Never used him. Stealing is useless, aside from certain exceptions that are few and far between, and still not worth the effort. Otherwise he was a basic swordsman, psh.
Edgar: F'ing Chainsaw. That's all you need to know.
Sabin: Nice techs, but I wouldn't necessarily choose him for that. They were all OK, until you decided to go and get Bum Rush.
Shadow: So he can throw stuff. Unless you want to buy special items just to chuck at enemies, the hell with that.
Relm: Best magician in the game? Ok.
Strago: Not sure how he even sticks out. He's a kind of magician, but Relm is better, so no one cares.
Gau: I found Gau to be one of the least useful characters. You'd have to go through a ton of sh*t to get him good skills, and they weren't even all that great. Some think they were, so his usefulness is debatable.
Umaro: No contol over what he does? No one cares.
Mog: Dance is nothing more than a special magic thingy. Nothing to see here.
Setzer: Like Cait Sith's Limit Break, Setzer's tech is about as yielding as... well, a slot machine.
Cyan: Ok, here we go. Strong sword fighter, OK mage, with a kick ass tech to boot? I'm in. Offering, Genji Glove and Quick = pwnage.
Gogo: Mimic? Depends on the other party members. Debatable.
Celes: I didn't see much of a difference between her and Terra. It was one or the other.

Just as a disclaimer, I don't hate any of these characters, and FFVI is better than cherry Coke. Which is pretty damn good.