I have had dinner at both and although I like the food at Coral Reef, I love the atmosphere at 50's. The food at 50's is more down-home cooking and the CR is a bit more better dining (I can't call it fine dining, but it's fancier than 50's).
If I had to make the call for myself right now, I'd go with 50's.
Regardless of what you decide, have a great meal and a wonderful vacation!