I've only ever disliked one squad-mate in a BioWare game, and that's Sera from DAI. She's uneducated, willfully ignorant, narrow-minded, obnoxious and doesn't follow orders. That covers most of my dislike. Still, all that said, I bet I could learn to like her if I could bear to play the game again. It is not my cup of tea, despite some great characters and lore.
I feel like fan-service really hindered Mass Effect. Tali's presence on the SR2 in Mass Effect 3, rather than being with her fleet, is one example of narrative being sacrificed for fan-service. There are other examples. I like Tali, but that was silly.
I've been playing DAI almost non-stop since it came out trying to make myself fall in love with it the same way I do ME... but I just can't. It's beautiful and the characters are somewhat compelling but the Inquisitor feels like some no-face, nobody and the story is weak enough without it being watered down with hours of insipid sidequests between main story missions. I think maybe I convinced myself I liked the Dragon Age series more than I actually do because it's Bioware and I ended up getting hyped for a game that ended up being just... OK.
As for a Sera, as an English person, to me, the way she talks makes her sound mentally handicapped and she can't decide if she's from the North or a cockney. It is just... bad. The way she says "Right?" and "Yeah?" after everything she says... ugh. Oh and I took her and Vivienne out with me yesterday and she literally farted, Vivienne smelt it and was quite rightly disgusted and Sera just giggled like a 4 year old. I thought, "What the hell am I playing??"