I quite liked these guys
Umaro - I just love this guy. Bugger all story but fighting with him (and fighting was most of the game for me) never got old. Highest level character in my game!
Celes - Easily the best of the lead characters. Had a good story and just came across as a likeable character.
Shadow - These kind of enigma characters that finally have their story shown are always pretty awesome. Loved Interceptor, too.
Edgar - If this game were expanded upon so that every individual got to show off his full story, I feel he would be my favourite lead character. I just liked his general attitude throughout the entire story.
Gau - UWAOOOOOO! Incredibly charismatic for a wild child. Just really enjoyable, a very uplifting character compared to most.
Sabin - Like Edgar, I feel I'd like him even more if his story was expanded upon. He does make me glad that there is no voice acting because I feel that voice acting on him would probably make him terrible.

These guys weren't bad either
Locke - Had too much of an Aladdin thing going for him for me to really enjoy his character, but he was good and I wouldn't have minded seeing more of his story on occasion. I just felt that in a lot of situations the things he said didn't really suit the character I wanted him to be in my head.
Setzer - Had a decent balance to him, I guess. Nothing I didn't really like about him, and anyone who flies an airship can't be all bad.
Relm - She's got a likeable fire to her. I liked it.

They were okay, I guess.
Mog - He's a fun little dude.
Strago - Just didn't see enough of him in the game to really enjoy his little story, I suppose.
Cyan - The speech was amusing for a little bit, and a very noble guy which I always like, but after a while the gimmick got old.

Glad to not use these characters often
Gogo - This guy has absolutely nothing that interests me. Mimic was vaguely useful but not very often.
Terra - I found her offputting. She is a constant downer. I mean, I know it's story related and she has reason to be sad, but that doesn't make her any more likeable. I found pretty much nothing whatsoever that endeared her to me in any way at all throughout the story. There was probably something, maybe, somewhere in there, but I honestly can't think of it. The good memory was probably drowned by her emo tears. =|