I like HK-47 and Canderous. Carth and The Handmaiden are tied for third before I make Handmaiden a Jedi.
I have to go with Hk-47, who could deny the blaster ready robot?
I'm tempted to vote for both Mission and Hanharr, but since T3 as no votes yet, T3!
To be honest, in a firefight, I'd take T3 over HK any day. Though HK is great for comic relief.
I always thought that Mission should also be considered Force Sensitive next to Revan, so I cheat and make her a Jedi Sentinel with the save game editor once I reach Dantooine. It's is if she's training with me.