I'd go with Artist Point at the Wilderness Lodge. The food is out of this world and the atmosphere is really quite and romantic. They have beautiful views of the waterfall and courtyard area. Also, you could take a nice romantic stroll around the lodge and the grounds after dinnner. It's such a lovely place.
Artist Point is one of our favorite places for a nice meal, because it is not nearly as loud and hectic as some other restaurants. For instance, we LOVE the food at Flying Fish and Spoodles, but they are both really loud and busy.