I have to admit I honestly had to think about this. We really like both, but I went with LeCellier for slightly higher food quality. Atmosphere hands down Coral Reef.
Coral Reef, hands down. THe food is quite good, we love the appetizers and desserts. Atmosphere is wonderful, especially if you're anywhere near the tank. While we eat at Le Cellier every trip, it seems a little crowded and cramped by comparison, with no view to admire while waiting for your meal. The food is OK, but frankly it's just as good at Outback.
Our last trip, our whole group enjoyed Coral Reef more than they did Le Cellier. I was a bit disappointing to go back this last time, compared to 2005. We had great service, great food, and a great atmosphere at CR. Try it!!! I'm sure glad we did.
ktink, my vote is for dinner at CR b/c I can't imagine walking around the park after having an app, entree, and desert unless someone is rolling me around. But we usually have our big meals at breakfast and dinner. Dinner is just a nice was to wind down and visit about the day.
Check this recent Coral Reef review: http://www.wdwinfo.com/reviews/coralreef.htm