I love the female trooper's voice, mostly because it's hilarious how much of a 1:1 it is for Shepard. The first time I played her, my fiance popped into the room, frantic and confused, asking "WHEN DID YOU GET MASS EFFECT FOR PC?!"
On the topic of troopers, though, I love whoever did Jorgan's voice. He's definitely my favorite companion, when it comes to voice.