... none? I really can't think of any squadmate in ME2 I'd want to kill. Jacob is the only one that I come closest to really disliking, and I'd just stick him on a shuttle to the nearest Cerberus facility.
I mean, yeah. Jacob's bland, but he's not a bad character (and I don't mean bland in the 'flatter than micron-thin paper/Bella Swan' sense. He's just... the closest thing to normal in a crew of aliens/freaks).
Jack's insane, but frankly, it's a wonder she's capable of interacting with people, period. As others have pointed out, everything about her is just a front to keep from letting her past overwhelm her (even the tattoos, it appears). And yes, she doesn't get all that better, even after her loyalty mission. Why would she? You don't get over traumatic events in a day or so, it takes quite a long time. I'm very interested to see what they might do with her in the third game.
Samara's ancient, has had a lot on her mind for the past 400 years or so. She also has to follow a strict code of conduct. She's been trying to kill one of her own children for just that long, and has had to lose her mate and other children because of it. A lot of it boils down to the fact that she's one of the most alien squadmates you'll get, and that's counting Legion. Hell, she even admits that her code can be a bit... messed up at times, but it works for her.
Miranda's a very interesting take on the idea of a 'perfect' character, and while a bit of a condescending ***** at times, it's just a personality flaw that won't go anywhere. She's also a devoted (if not somewhat misguided) sister, her loyalty mission is still one of my favorites. She thinks she knows everything, and that just makes the times when everything goes completely wrong all the more satisfying. Grunt, despite being created to look like an adult, still has the mind of an infant. It comes across very well in the game, and I loved when you could go talk to him and he started to actually understand things and form his own ideas, rather than just going on his imprinting.
As the others tend to get very little hate, I won't write up any justification for not wanting to kill them. Never got any of the DLC, so I can't say anything about Zaeed or Kasumi.
The only person I can think of wanting to see die would be Conrad Verner. And even then, only if we got to see the Eternity bartender beating him to death with his own spine. ... maybe Morinth, if the controller ever slipped and I accidentally picked her over Samara.
