Basically it boils down to:
What kind of RPG do you like?
Old School "proper" RPGs? Clearly you will enjoy DA:O.
Action RPG? Clearly you will prefer DA2.
Do you have the ability to enjoy a depressing and dark adventure?
If not at all? Neither game is for you.
If yes, as long as the game has strong silver linings: DA:O, but not DA2
If yes, period: Both games.
Do you prefer voiced protagonists?
Doesn't matter: Both games, obviously
And the last one is very subjective and just put here because I enjoy ranting:
What kind of companions do you prefer?
Well written characters with unique backstories and compelling personalities? DA:O
Badly written Emo characters with too much JRPG influences and carrying idiot balls the size of an arch-demon: DA2.