I would stick to Newmar, Holiday Rambler or Tiffin. Also, stick to Freightliner or Spartan Chassis. They are two of the biggest chassis manufacturer and you will find parts and service easily.
The engine being out back makes it quiet up front. Mine has a rear radiator, and like others have mentioned, that makes engine access limited. Try and find one with Cummins ISL 400HP engine and side radiator.
Mine has a 275 HP 5.9 ISB Cummins and it runs great. A little underpowered in the big hills, but I have been coast to coast pulling a crew cab 2500 diesel Chevy truck and it will go up anything.
These are comfortable to drive, especially if you find one with independent front suspension. Hope this helps.