I. Garland. Although if we're talking design, I think the Fighter's in the NES version was nice.
II. None
III. Good grief, Cid maybe? There's not much characterization in this game. But, I do like the designs of the Onion Knights, they're pretty cute. Battle-wise, probably the Warrior.
IV. Edge or Rydia if we're talking battle. In terms of character, probably Rydia? I found her backstory very sympathetic.
V. In battle, since there's classes in this game, the Blue Mage. I even made my party members all Blue Mages at one point. I liked that you could learn certain types of magic from enemies. That was a really neat idea! In terms of character, probably, Bartz. I found him relateable as he felt to me like he was this guy who was just wandering around, and then one day he ends up on a journey to save the world. I like how laidback he was, while he could get serious, he never really lost his easygoing nature. I also liked Faris, but not PS1 translation Faris.
VI. In battle, Gau. Gau is one of those characters that can either be really good or really bad. And the only way he is the latter is if you never use him at all. If you raise him well enough, he's a freaking tank! I think it's especially kind of funny how one of his strongest Rages can be learned from him jumping a Stray Cat. Idk why, I just do. In terms of character, hard to say, Celes and Terra had good character arcs, Locke was a funny character with a sympathetic backstory, Edgar was...Edgar. I can tell you who it isn't though, Umaro. Mostly because getting him was a pain.
VII. I, for some reason, can never beat this game. But, I have gotten to a point where I can safely say that it's Tifa. In battle, definitely Yuffie, say what you will about her character, but her limit breaks rock!
IX. I like almost all of the characters except Amarant. My personal favorite was Zidane, as despite his somewhat perverted and rougish nature, he manages to come across as a rather sweet guy and a good friend. I especially liked the "You're Not Alone" scene, as despite the identity crisis Zidane is having at the time, his friends stand by him. And the reason for that is primarily because he helped them when they were going through their own respective rough patches (except Quina who had none, s/he was still funny though). In battle, Vivi, I remember this one moment back in Mount Gulug, when most of my party was dead except him and I was fighting those dragon enemies. And Vivi managed to save my butt that day.

These are from the ones I played anyway.