We haven't had any issues with our 2015 Alpine that we didn't cause ourselves, or at least anything worth bothering with warranty on. We bought it in 2016.
The one exception might be leaking hydraulic cylinder which was covered under warranty, but that is more Lippert's fault than Keystone's.
We had a 2014 Hideout previously, and aside from a missing shackle bolt on the rear axle from the factory (a huge oversight, in my opinion) it was problem-free. We had it for a year, then traded to our first fifth wheel in 2015.
The 2015 Crossroads unit we had between the two Keystones was nothing but trouble, and we ended up trading it at a loss just to get out from under it with all the problems it was having. It spent more than half the time we owned it waiting on warranty repairs for the roof, the axles, electrical and so many other issues that I can't even remember them all.
We've done a ton of upgrades on our Alpine and would probably sell it to buy a Luxe or New Horizons now that we're going full-time if we wouldn't take such a hit on depreciation and modifications. But as far as the mass produced units go, we think it is probably as good as any. We make it a point to talk to owners of other rigs at sites and have talked to plenty of people with DRV, Grand Design, Redwood and other units that have experienced more issues than us. When we took our rig in to have a FlexArmor roof put on, the rig in front of us was a brand new Redwood that had the roof bubble up and blow off going down the highway. Our roof replacement was our fault (sort of), due to a low hanging tree branch that tore it going into a campground.