For Imps I'd say:
Bounty Hunter: Skadge
Weird, on my agent I only use Vector, but then I am a healer. I guess if I went sniping I'd probably use Dr Lokin as I adore his voice. I would never ever use whiny, needy, sucky Temple though, she really grates on me.
My Smuggler groups with Guss despite having HK; Bowdar and Risha, never used.
Other alts are too low and so only have 1 or 2 companions at the moment. I think Qyzen will be a keeper on my Sage though, I quite like him.