My advice is sci-fi for DHS. The only other restaurant there worth the cost and time to eat there is Brown Derby.
I'd do Cape May for Epcot - its at the Beach Club. Its fairly quiet, the food is good, and the characters come around more than once usually. We try to fit this in at least once a visit for either an Epcot or DHS day.
Keep trying for Garden Grill - it will likely open up. You might be able to get it with a processional meal. We had to do that last December. People will cancel 45 days out, so just keep trying. I managed to snag both Le Cellier and GG by just calling at least once a week to see if anything had opened up.
Other Epcot restaurants I like are Coral Reef (service can be spotty, but the food is good - just not a place if you're in a rush), Marrakesh, and Rose & Crown. I haven't tried Akershus yet, but was disappointed with France and the rest I can get better food at home. Also, keep in mind you can go out the International Gateway and get to Kouzinna, Cat Cora's really good restaurant at the Boardwalk and Yachtsmen at the Yacht Club (enjoyed this more than Le Cellier). Yachtsmen has a dessert for kids that they can paint themselves - I saw the kids at the table near ours REALLY enjoying it.