Lt Kurin probably had the biggest ratio of impact:screen time for me. The decisions she was forced to make on Thessia were incredibly tough.
*Puts flamecloak on*
I never really got why everyone loves Kal'Reegar so much. His American-as-apple-pie accent sticks out like a sore thumb amongst the Quarians and - let's face it - he doesn't really DO anything. Of course, the fact (IMHO, of course) that Adam Baldwin is an intolerant, redneck douche is probably coloring my judgement. And before you flame me for that last comment, go and check out his twitter page.
Speaking as a liberal dude who's not very fond of conservative libertarian types, Adam Baldwin doesn't fit your description at all.
He's a conservative, and a libertarian. But he's not that bad of a guy. As far as social issues go, he's pretty liberal. He has a strong respect for the military (tending to play military characters), and his stances take a lot of political realist positions, which I do disagree with. That said, he's not a bigot, and he's certainly not an intolerant redneck (he's from Chicago after all, one of the more traditionally liberal cities in the US and an island of blue in a sea of red). He's also willing to be respectful to other people's views, and he got along very well with his cast-mates on Chuck and Firefly, all of whom are pretty liberal. Nathan Fillion refers to him as one of his best friends. And you don't argue with Nathan Fillion. He's also willing to poke fun at himself.
As for Lieutenant Kurin, her decisions really weren't that difficult. Get to the temple at any cost. You can do it, or you can complain about it.
I prefer to focus on the task ahead.