Duncan! Duncan, Duncan

for an easy first place. I always try with my human noble, one day I'll break him
Then, in current order:
Loghain -- naughty in a "oops i killed the king, did i do that? " way, plus the voice....rawr
Roirdan -- sexy accent so smooth and understated it melts butter -- he purrs
Sten -- cause i love my mod, and I always travel with cookies.
Of all people, Ser Otto. Seriously, that man has a mouth. Plus, great likelihood of being good with his other senses
If I had to pick one, Duncan. Loghain is close though - once I talked to him a bit I just loved his dry wit, the sarcasm worked for me

I'd love Riordan following me around the game though, doing color commentary for me
just to hear him. His voice is simply perfect -- so low it almost makes you lean closer to hear him clearly...
Slightly off topic: A character I really liked though was the very flamboyant blood mage in one of the alienage quests late in the game (found his name, Caladrius - which is a very interesting name to have chosen, given everything...). His body animations, mannerisms and voice were just priceless. As a companion someone like that would have been an absolute riot to travel with

I kept imaging him, in a very dramatic oh-woe-is-me tone, to say " Oh DRAT. Now look what you have gone and done...I chipped a nail. " ;-)