As others have said quality is equal thru out the RV industry. Unless you want to pay over $100,000 for a 5'er and that still doesn't guaranty quality it just means the better equipped 5'er will have problems also, then look for a floor plan that works. At our last RV show there was a dealer that started to carry the new Grand Design 5th wheels. We went to look at then specifically. I didn't see anything about them that said they were built any better than any others. They have great floor plan but the cabinetry was still on par with the rest of the industry.
Of the 3 you listed I would go with the Montana since you can get the Glacier insulation package as an option. You only get R9 walls and R14 ceiling and floors in the Heartlands.