Get a class C that's built on an off the shelf truck chassis (usually Mercedes Sprinter or Ford E-350/450) and at least the chassis will be reliable. You'll still have to deal with problems with the RV parts but at least you'll be able to drive it (unless your problem is that the slide-out won't retract)

I agree with this statement and I should have been clearer previously. When I complain about build quality and lack of innovation, it is solely with respect to what the RV assembler does with the Mercedes or Ford chassis.

it's better to build on a spartan or freightliner chassis

It all depends on whether it's a class-C type cutaway where the cab is built by the chassis manufacturer (so you get a steel cab plus airbags and other safety features), or a class-A built on a stripped chassis where everything but the frame and engine comes from the RV manufacturer -- many of those are essentially a lightweight box on top of the frame and will disintegrate in a crash, and you'll likely not survive a rollover crash. Even with a cutaway chassis, depending on how much of the cab they cutover for cab access, you may not fare too well, but much better than with nothing but a wood and fiberglass box surrounding you.

With a cutaway, the manufacturer takes care of all of the steering linkages, driving controls, etc so you have some assurance of quality -- everything related to driving is built by the company with the most experience in building trucks and cars rather than the RV manufacturer.

I don't know what you get in the $300K+ Newmars and other expensive rigs since that's way out of my (and most people's) price range.

Yeah, one of my friends just bought a brand new RV (I don't know the details), but spent basically a month after purchase getting a whole bunch of QA fixes made, from the minor and cosmetic to fairly major.