Dragon Age: Origins is apparently a very good game (Simon wants this one really bad, lmao). But I've played Assassin's Creed II, and it's lots of fun. In the first five minutes you can tell this has surpassed the first by miles.

I would personally go for Assassin's Creed II, as it will be easier for you to get into and then get Dragon Age: Origins at a later date. Same goes for Resident Evil: Dark Side Chronicles, even though, personally, I don't give a shit if I never get it >>.