Sera. I dislike children, and she is not only a child, but a brat. Apparently she has some less-immature moments, but those aren't remotely enough to make me want to have anything to do with her. Plus, I just can't shake that "by a straight dude for straight dudes" feeling.
Number two is Vivienne. I wanted to like her and her awesome Maleficent horns, but between her attitude and the feeling that I can't really trust her because, hello, career politician -- it didn't work out at all. She just doesn't fit in, nor do I get the impression that she wants to fit it. While she does give some good advice at times, she's not someone I'd want to share a tent, blanket or tankard with, nevermind a raw emotional moment. Yes, she honestly wants to help, because no one with two brain cells to rub together wants Corypheus to win. If that means mingling with unwashed, uncultured lessers, she'll do it and try to rub some culture off on them in the process while using what influence she can wring out of it all for her own gain. That's not exactly a good basis for friendship or we-have-each-other's-back-without-hesitation battlefield trust.
Number three is Iron Bull, because he's an enemy spy. Self-admitted, which is gutsy, but still. While he has his good moments and definitely tries to fit in and get along, I didn't really start trusting him until after his personal quest which I resolved in favor of his Chargers without a second thought. Doesn't help that I don't like melee DPS in this game, so I have no reason to ever bring him along.
Mind, the only one I really dislike in pretty much every way is Sera. I can respect Vivienne and Bull, I just am not keen on them. Overall, though, they did a pretty damn good job with the characters.