Best/Worst Origin?
I really liked the human noble and dwarf noble stories. The human noble in particular ties into the main story well and it was pretty epic finally getting revenge on Howe. Same goes for the confrontation with your brother as the dwarf noble. Both really cool showdowns that you can leave towards the end of the game and give you the sense that you've come a long way in the narrative. I also love the dwarf noble origin story in particular simply for how hilarious it is to be a royal *beep* to all the lower castes, like not deigning to speak with them and getting your bodyguard to do it instead. It feels so right.
The Dalish is easily the worst. The origin story itself is alright, but it really bothers me how the Dalish is the only one that doesn't give you the option of returning to your roots/dealing with your past in a significant way, since the Elf tribe you encounter later on is a different one to your own. Instead, all that happens is a very weak sequence where your old friend Tamlen is part of the Darkspawn attack on your camp, which felt extremely random and tacked on. You kill him, Alistair is . . . and that's pretty much it. It had virtually zero impact on me.
(I'm aware you do return to the story of the mirror in Witch Hunt, but I haven't played it yet).