Although he has no cool sidequest or whatsoever, taking him in my party just gave me that SW feel again.
I made him a dual-wielding slayer of all, with Bacca's blade and Mission Vibroblade (for story roleplaying reasons, obviously). When entering a fight, I can only imagine the thoughts of the poor (in many cases, Sith) enemies.
"Okay. There's a Jedi. Let's gun him. Wait...what's that behind him?!"
*Sound or arms being ripped off*
Carth on second place, now that his backstory is explained in the Kotor comics. He helped Jedi before, so I alyways repay the debt by equiping him with Mandalorian armor and weaponry