We have eaten at both. Let me just start by saying our entire family of 7 voted Garden Grill the worst food of our Dec. 2007 trip. Character interaction was very good but the food just ruined the whole experience.
Coral Reef has an awesome setting. The food is consistanty enjoyable. We all loved it, and are returning in 2 weeks. We recommend the lobster bisque, cod cake and catfish.
Not even a close call in my opinion.
Mrs. Disney Ron