Dragon Age 2. Fans of gigantic AT-ATs, Jedi Knights and ancient Qui-Gons would be better suited for the Lego Star Wars 3: The Clone Wars demo. (Note: Qui-Gon Jinn probably isn't in this game. We just needed the symmetry.)
The demos are available now on XBLM, and will arrive on the PlayStation Store later today, following the weekly PSN update. The demo for Dragon Age 2 will also make its way to PC sometime today -- we'll let you know when it shows up.