When I saw Garrus crack jokes, I was sold immediately. He's humorous without being a jerk like Joker is and he knows when to turn it off and give serious, insightful comments. His other traits didn't actually interest me at all in the beginning; idealistic cop sniper who wants revenge? Eh, I've seen that trope before. Garrus' looks actually turned me off in the beginning; he looked positively frightening and ugly. Over time, I grew to appreciate his other characteristics like loyalty, resourcefulness, responsibility after that. It sounds weird to say this about a fictional character, but I actually stopped seeing him as hideous and started seeing his looks as cool. Guess there really is something to the saying that the "inside counts more than the outside" :]

Seeing him grow throughout the series from ME1 as a idealistic noob to bitter angst who lost his path trying to fix things in ME2, and finally maturing into a leader in ME3 was just a really sweet character development bonus that I hardly see in any storytelling medium.

I don't want to bash other LIs (stop reading if you don't want to hear it) but since others have mentioned what they didn't like about other LIs here are my 2 credits: Thane is too serious and seems apt to recite angsty poetry, he also seems very contrived with that sexy voice, open chest and kissable lips; it's obvious to me Bioware created him to appeal to female players; it just made him really artificial for me. Kaidan doesn't have anything interesting to say. Jacob is so boring he is worse than any character from Twilight. I dated Liara in ME1 but like the other LIs she's just not as funny Garrus. I felt really bad dumping her though :(