Yeah, I didn't dislike Sebastian. Like Bethany, he was too inoffensive to dislike (or to like, for that matter). I did enjoy trolling him, though, and I actually kinda liked him when he flipped his sheets over Hawke sparing Anders, but 30 seconds of "Wow, Seb, I didn't think you had it in you!" isn't enough to overcome two acts of "What's the point?" So I guess my biggest issue with him was that you could tell he was an add-on. It was always a question of bringing Sebastian or bringing a companion who participated in the quest, so Sebastian spent the game on the bench, sadly.
Actually, I didn't hate any of the winning/losing team. I flat-out adored Carver. Yeah, he's grumpy, but I understood where he was coming from. He seemed very genuine, as were his loyalty and his love toward his family. I have complex feelings about Vivienne, but at the end of the day, her I find her imperiousness entertaining. And Hawke was probably my favorite protagonist, so no hate there.
If I were to pick my own Ultimate Nadir of Dislike team, it would have to be
--Warden. I used to like her, but the hyperbolic praise the HoF receives only served to remind me that she didn't really have a lot of personality to begin with.
--Oghren. I don't dislike him, but I do dislike the way he was portrayed. Alcoholism isn't a joke. I wish the subject had been handled with more sensitivity.
--Leliana. There's a word for something that's bland and sweet without spice or acid to balance it: cloying. Leliana is cloying.
--Velanna. This was a hard one. I get where she's coming from... but she just isn't a sympathetic character for me. YMMV.