I love several of the characters in the ME universe and usually for different reasons.

Miranda: Miri made a huge impact on me during the project Lazuras escape. I loved her cold, competent persona. I was instantly drawn right in. It gave cerberus a kind of personality, a credibility with someone like miri backing it. Pieces of her came together after jacob and her LM, as well as conversations throughout the mass effect 2 game. She's the first and probably only LI that I feel is sheps equal. And I love that. a lot.
Wrex and by extension the Krogan. I loved him in ME1, he was pretty straight forward and didnt pull any punches. The confrontation made me respect Wrex more, he knew what was at stake, but to see Krogan and the genophage cured he set aside his merc attitude and stepped up to defend the Krogan mantle. that continued into Me2 where he becomes a visionary and through krogan ideals, like strength, begins consildating the other krogan clans. Epic
Legion: He blew me away and I didnt see him coming. his conversations were utterly fascinating, and made me think about the idea of evolution; the conflict between the quarians and the geth and I just want more. I love how the Geth operate, though they do seem to feel their end lies in becoming a reaper of sorts, themselves. Minus the "reaping" aspect, or so I hope.
Garrus: his path so far has made sense, he was so frustrated with C-Sec, it made sense that he ended up in omega. Im hoping between my influence with Dr heart and Sidonis, he evolves past his flaws from the first two games, I hope he becomes a spectre- but more in line with my shep (paragon) ideals, then say- a saren esq spectre. for the sake of his overall well being I guess.
Mordin. The moral ambiguity of miri, and the creativity of Legion I love his character. Though Ive tried to avoid leaks and what not, I think I see where his character is going in Me3. and im happy. By extension, the salarians, I love their species. Its fascinating to contemplate how their short life spans contribute to their mentality.
Tali and by extension the quarians. I won't say too much about tali her as this is a miri thread, but Ill admit Im having a really hard time deciding on either her or miri for my main canon. I love the quarians and their past, and feel they are a truly unique race.
Other noteables, Jack- I get her. And like her after several conversations. Samara, Love her hardcore, her ideals and black and white extreme value trotting persona is just damn sexy. Kaiden, jacob, are well adjusted bros in battle. Thane is interesting mainly because of the drell, well him too actually. grunt, love his story. Liara is- decent. Ashley is probably my least favorite. I think in large part the romance is really thrown on you by just being friendly to her and having a conversation. So by time she was citing me poetry, i was thinking, WOAH, hold on a sec. Im not that into you, keep that crap to yourself.
just some random thoughts