I think every squadmate from ME1 and 2 have their merits, and therefore I dislike none of them.
Kaidan- He seems sincere enough. I think his backstory is interesting, and he just seems overall like a long-time associate of my shepard and a general good friend.
Ashley- Straight-up honest. I did find her candour a little grating at times, but I could respect it. I still choose Kaidan over her at Virmire, however.
Garrus- I love the 'bro' feel he has. A truly good friend who has some very well-crafted dialogue.
Wrex- Shepard. How can anyone not like him? His brutally simplistic way of looking at things is awesome.
Tali- She feels like a little sister through the whole series. I end up feeling very protective of her.
Liara- Again, a bit of a sisterly feeling there. Her pronounced role in later installments is quite annoying, but I try to look past that.
Jacob- I think I'm in a minority of people who like him. He has a backstory I can relate to, actually, so I find him a very realistic character. Also, he's honest and open, a big plus.
Miranda- Initially, i hated her. She came off as cool, aloof and arrogant. However, I gained respect for her after taking her to face the Human Reaper, and when you look at her character from a more objective viewpoint, she's a pretty good addition to the series.
Mordin- He felt like an old uncle to me, full of stories, easily sent off on a tangent, and very funny. He lost a lot of oomph when they changed his VA.
Grunt- I look on him as shepard's student, and love seeing him grow from bloodthirsty killing machine to bloodthirsty killing machine with a purpose.
Jack- My Shepard's LI, every time. Her complexity is just hypnotic. I'm disappointed with her portrayal in ME3.
Samara- I love the mysticism behind her. She lives by a clear code, and her integrity allows her to commit some emotionally difficult actions without question.
Thane- The tragedy of this character is enthralling. It particularly hit me when he said shepard was the first friend he'd had in a decade. With both him, samara and Mordin, their spirituality really struck me, actually inspiring me to be a better person for it.
Legion- My word, the machine perspective they give is amazing. I loved having the view of a splintered consciousness on the ship. I was disappointed they needed them to go through a pinocchio story in ME3. The character lost its oomph.
Zaeed- He makes me laugh so much, and his war stories are brilliant.
Kasumi- A bright, tinkly character. You need a little light-heartedness in such a dire situation.
In short, I think all the characters were amazing in ME1 and 2, but I think they all suffered in some way by being included in ME3. The characters are just... lesser creatures in the final act. And as for the two introduced-
Vega- I'm sure he would have been fine, if we'd been able to talk to him properly for more than the scant conversations we got. as it is, we don't know a lot about him, and what we do see is him being rather insubordinate. Even disloyal characters in ME1 and 2 don't treat the Commander like that.
EDI- god no. We did not need boobs on the ship. This was a lame twist to pander to those who want Joker to bang the ship. The character is less for it.
Traynor and Cortez- I liked them. There's enough conversations to really establish them as people to be concerned about.
Allers- People may mock me for saying this, but she had the potential to be a good character. If they had put the work into fleshing her out into a proper character, she'd have been fine. As it is, she only just begins developing who she is (colony kid from Bekenstein) moments away from the end. Because of that, it makes it clear she's an attempt to opander to the crowd by putting in a recognisable face (not to me, though. Never heard of Chobot before now).
I've never recruited Morinth, and I didn't buy Javik, so i can't comment on them properly.
In short:
Love: Kaidan, Garrus, Tali, Wrex, Jacob, Miranda, Mordin, Grunt, Jack, Samara, Thane, Legion, Zaeed, Kasumi
Don't care: Ashley, Liara, Cortez, Traynor
Actively dislike: EDI, Vega, Allers