It's all relative.... but I have done direct comparisons back to back on several of my own setups. I have owned 3 GXs and driven them both back to back with the one I keep around that has the 5100s.
The best ride quality is 100% STOCK with low mileage. These trucks drive the best in stock form, hands down. Problem is it's nearly impossible to find one with fully functional airbags/adjustable dampening, etc. so most people don't know what that actually feels like. I have a rig right now with 80k original miles and it is the best riding and handling GX I have ever been in. They did it right from the factory.
My Dobinsons "comfort" setup (2"/1") on stock sized load range C AT tires rides just like stock but handles like a wheelbarrow. Very soft ride but very noticeable roll in corners. Wasn't much taller than stock.
Bilstein 5100s with load range E AT tires rides like a damn skateboard, but handles far better than the Dobinsons comfort. It's harsh as it gets. Not quite leaf spring harsh, not solid front axle harsh, but relative to stock it rides like s***.
Bilsteign 5100s with load range C tires is still noticeably harsher than stock, but not as bad as with the stiffer Range E tires. Handles okay. This is the setup I keep around, mostly because it was the cheapest of them all and I can't make any money if I sell it. If I built this truck over again, I would NOT buy Bilsteins.
Regarding KYB, I have had their shocks blow out in 30k miles too on an old Xterra I had. They're all junk until you get into the higher end brands like Dobinsons/OME.
What's harsh to me may not be harsh to you, and vice versa, but my relative comparison (same day driving) is factual.