For multiplex theaters downtown you really only have the choice of going to Pacific Place (AMC) or The Meridian (Loews). Each theater plays different movies, so if you want to see a specific movie, you really have no choice. Pacific Place seems to play the more popular movies, which could be good or bad depending on what you are in to.
Personally, I prefer the theater at Pacific Place, but like the snack bar at The Meridian better. The great thing about the Pacific Place Theater is the parking garage. Parking is cheap after 5:00. I would suggest parking at Pacific Place, even to go see a movie at the Meridian. They are only a block away from each other.