Wow. Trying to comb the soundtrack to pick a favorite is hard. It would be easier to pick out a song I don't like...because there really aren't any. xD
Though I'm not sure if my very favorite bit has a place in the OST or not. It is part of the random music you hear throughout the game, but it is definitely from 'The Dawn Will Come.' It's where the brass joins the chorus with that heavy 'For One Day Soon' and then eases off to let the (I think it's the woodwinds...things are getting a bit muddled listening to the rest of the soundtrack while I'm typing this) others back in for 'The Dawn Will Come.' Still gets me. And it was something I picked out early as a favorite because I'm sure they had it playing on a twitchstream at least once. It appealed to me instantly.
As to the why? It's something in the chords. How it builds up and the brass is just rich and lovely. I used to play trombone, so I've got a soft spot for loud things like that. And I'm sure I'm doing a poor job of describing it, but it's really a good bit of music and I enjoy it a lot.
And it's come around to the tune I 'love to hate' and constantly hum at work: The Orlais Theme. (Empress of Fire in the Reign of the Lion do-do-doo~and I don't know the rest of the words~!) It's so good! But it's far too catchy and I really wish Maryden would take requests because I do not want to hear 'Empress of Fire' or 'Sera Was Never' every time I go into that tavern. Seriously...you're creeping the poor woman out with that song, Maryden. I would really like to hear 'Samson's Tale' more than once a playthrough.