I have played the demo for both, and to me, Bioshock is the clear winner of the two. The atmosphere created by the environment really gets into your head. Not too mention a Big Daddy named Mr. Bubbles. Clearly any game with a hulking behemoth, who has a drill for an arm, and goes by the name of Mr. Bubbles is a winner in my book. Plus I thought the Blue Dragon demo was kind of boring imho.