I can think of a couple characters that I disliked. There arn't a lot of FF characters I hated...
Dislike:
FF7:
Cait Sith: Ok, first off, he was a horribly placed character in the game. He was statisticly horrible, his limit could end your game, and he really is only noticed for stealing the black materia.
FF8:
Rinoa: Yeah, I know she's one of those princess' in distress... but she could have been a little more calm about it. She would always get too emotional about things and reminded me of a bad soap opera I once watched... xp
Irvine: Well, the only reason I'm putting him here is because he really didn't have much to do in the overall story plot. He's a cool character, but he wasn't needed.
FF9:
Armarant: *Points to irvine and cait sith areas*
Eiko: I didn't like her. She was like a little girl with a constant sugar rush. She also acted like a complete baby.
FF10 and 10-2:
Wakka: Ok, so he is pretty strong, but he really doesn't end up being one of your key warriors in the end. (Unless you do some sphere work with him)
Seymour: Creepy. Very creepy. He wanted to marry Yuna. End of story.
Brother: I really don't know what was wrong with him, but he always acted like he was intoxicated with something. He make FFX-2 sorta funny, but otherwise, he drove me crazy with his constant stupidity.
Hate list:
Quina and Kimhari: Ok, first let me point out that both characters are blue mages. Blue Mages only become useful when they learn blue magic. That whole blue magic thing acted like a side quest that just made the game more annoying. Second, Quina and Kimhari were the worst characters in there respected games. Quina used a fork to kill his enemies and did little damage. Kimhari just became a ghost of one of your characters on the sphere grid. So unless you did MAJOR catch-up with him, he was useless. Finally, both characters had one major boss battle that HAD to be completed. For Kimhari is was the Ronso brother reunion, and for Quina, it was helping Zidane get rid of Lich. I personaly hadn't used either character much so I hat to spend extra hours leveling them up. xp
Well that's about it. I'll go now.