I have not been to either, but looking back through past reviews, and at AllEars, it definitely seems as though Coral Reef gets more consistent positives, but that GG gets very, very highs and very, very lows and is a bit more of a gamble.
For the records, the Grill is the one restaurant that my sister and her husband rail against as their "horrible meal experience." (mostly re: the quality of the food). Such experiences happen at every restaurant, though.
Is this post useful? Probably not. Best I can say: aim for the atmosphere that intrigues you most.