Mako. Hands down the most annoying companion to me. You spend the entire time she's with you listening to her whine, complain and just overall needy behavior. Look, kid, I'm a bounty hunter. You knew that when you signed on with me. Quit whining and complaining every time I do my job. Gah. I just want to mule-kick her out of an airlock.
If I had to pick a second, it'd probably be Ashara Zavros. 'Don't make me go against my teachings." Ugh.... *slap*