FF1: Black Belt. IIRC he becomes a killer fighter at high levels but by the time you get to high levels the game's easy and at this point in the rpgs you don't have character development so all you have to base them on is worthfulness. Fail.
FF4: Edward. Although the new games increase his talent, this guy is made of fail. Weak magic abilities. Weak defense. Weak attack. Just plain weak.
FF6: Gau, but honestly I liked pretty much the entire cast of this game. I just liked him less.
FF7: Yuffie. I like my materia. I like it even better when it's assembled right. Damnation. Pain in the mofo ass.
FF8: Squall and Rinoa. Yes, I know they're the main characters, that's the problem. Too much teen drama crap for my tastes.
FF9: Quina. Okay, Quina's cute, downright bizarre. I get the point, it just didn't resonate with me. I don't give a shit if they are super-powered--I don't pick characters based on power at this point in gaming anyways.
FF10: Wakka. I liked him a wee bit but mostly he was just annoying. He seemed very one dimensional. The only part I liked was the part about what he had against poor Rikku, which I thought deepened his character, too bad they ditched that bit of interesting storyline.
Um, the others I haven't played well enough to get a feel for the characters. When I do I"ll edit.