Much like the way the Disney Robin Hood film simultaneously launched 10,000 furries, 10,000 fans of classic English literature, and 10,000 devoted Disney haters, Garrus's performance in both games was enough to win me over to the Turian cause. When you lump together nearly unpierceable skin, above-human physical and left-brain abilities, the ability to survive on half of the "uninhabitable" planets in the ME universe, and that kickass voice of Leigon/Robert Downy Jr. Talking into a tin can effect, and you've got something that could be conservatively described as "Made of Win".
Just...Daaaamn.
The runner-up is the Drell, thanks to those nasty little details about their near-extinction and their susceptability to gradual, painful life-sapping ilnesses.
Strike that: The runner-up is a standalone Geth Platform, like Leigon. Only, y'know...not broken.