I think SOME of the 5th Wheel trailers are great. Many have a great floor plan and naturally cost a lot less than an equivalent size Class A coach. If you travel like some people and go from A to B and sit for weeks/months on end, then a 5r may be your best bet.
If you travel like us, where we seldom spend more than a few days at one location, then a Class A was a better choice.
Set-up is a lot easier with a Class A but it comes at a cost, initially and with required additional maintenance to keep things operating properly. I doubt if there is much difference in fuel mileage but insurance costs may vary.