Seaworld, hands down.
DHS might be worth a few hours but Seaworld, with all the shows, the penguin experience, the sea turtle building and other stuff will keep you busy all day, even if you leave out the thrill rides. Living Seas at Epcot can't hold a candle to all that Seaworld offers. Plus you can take pride in the knowledge that part of your admission will go to helping Seaworld continue to do wildlife rescues and rehabilitations.