We have eaten at both of these restaurants. If you aren't going to be doing any other character meals, I would say go with the Garden Grill. The food is good and the characters (Pluto, Chip, Dale and Mickey) are dressed in their farmer/gardening clothes. The restaurant turns slowly and overlooks a couple of scenes from The Land ride.
If you have other character meals planned elsewhere, I would eat at the Coral Reef. The food was excellent when we ate there in June. The atmosphere is really neat for a 7 year old too. One entire wall of the restaurant is the Living Seas aquarium.
I think you would be pleased with either restaurant.