We went from a 5th Wheel to a MH, and don't regret it. Although you have a vehicle (tow truck) to use when your at a location. You could if need be tow a toad or tow dolly with a vehicle.
With the 5th Wheel the problems we encountered was when the slides are in you can't use the bathroom or Bedroom. And you can't always put the slides out, as in the case of a Florida rest stop with lots of trucks.. While with a MH you have thru access to the whole MH. Secondly, With a 5 you have to get out to enter the trailer a MH you don't. There is also the question of what tow vehicle do you plan to use? In my opinion anything less the a 1 ton dually is unsafe. And Diesel verses gas is always a debate with no real answer other than the opinion of the person and their equipment. I used a GMC with a 454 and averaged 10 to 12 mpg, using 87 octane at 3.40 per gal verse Diesel at $4.05. Gas is more economical and parts are much cheaper. Having said that my MH is a DP and I average 11 MPG so I'm happy with that..
There is also the fact that depending on the MH, you will have a generator where as most 5ers don't. I guess your own research will provide you the answers you seek, and once you have then re evaluate before your purchase.. Also think used !!!