I think what you're asking is very much a subjective thing based on personal experience. I've not owned a GD but I've talked to GD owners, dealers and their service depts. They all sounded to me about like what you find with Keystone - the dealer is going to make the difference and all units are made about the same. Remember that the folks running GD came from Keystone so doubt you're going to find much difference in the processes - and from posts I've seen on various forums that seems to hold true.
When comparing IMO always compare price points - not floor plans. Similar trailers from Keystone and GD will have the GD coming in several thousand dollars higher generally so typically you wouldn't (I wouldn't) expect the 2 to be the same quality wise - but they probably will be.
As I've said in the past, my only snafus with Keystone have been because of the dealership and Keystone has tried to help, although occasionally it takes a lot of effort and patience. I will say that GD will be on my radar when we replace this trailer but so far Keystone, to me, gives the biggest bang for the buck and the best floorplans. One other factor for us is the dealership network - there are far more Keystone authorized dealerships anywhere around us vs GD which is important.
Danny & Susan wife of 52 years
2019 Ram 3500 Laramie CC SB 6.4 4x4 4.10
2020 Montana High Country 331RL