I've done GG the last two times I went and neither time blew me away. While there were a ton of open seats it didn't mean we got to see the characters a ton of times (Chip and Dale twice) and the Mickey and Pluto once. The breakfast was for my family much better. We thought the lunch/dinner was okay but no food blew us away.
Tusker House has been amazing both times we went (lunch and dinner). We were in the side room and saw every character twice. The food was AMAZING and a much bigger variety. We have super adventurous eaters and very picky eaters and everyone thought it was amazing.
Pros:
GG: sit down and food comes to you.
TH: Buffet so you have to get up and eat it.
TH: Has a much wider variety of food from salad, meats, fruits, breads, etc.
GG: Characters Mickey, Pluto, Chip and Dale in farmer outfits.
TH: Mickey, Donald, Daisy, Goofy in safari outfits
I would personally always recommend Tusker House over about anything but certainly GG has a huge group of fans as well.