I absolutely loved Demons Souls unrelenting difficulty and the way it makes you fully appreciate every time you are able to get just a bit further in each stage. It can be a turn-off for some, but I truly enjoyed it. It is a unique and one of a kind experience.
From a storytelling and character development aspect Dragon Age Origins is amazing and the better of the two (IMO).
Tough choice, it is really a matter of taste. You really cant go wrong with either title. Sorry, I loved both.