The thing to keep in mind about motorhomes is very few ever get enough miles on them to reach the point where engines wear out. Instead failures are generally either due to lack of maintenance, or just bad luck, with a few exceptions. For all practical purposes any drivetrain combination will work, though some of them will be slower about getting you there than others, particularly if you travel in the western mountain states.
So as already mentioned maintenance should be one of your key concerns, the big issues tend to be leaks in the roof of an RV, and wear/aging of mechanical components, the big thing here is anything made out of rubber will tend to dry out, crack and fail somewhere in the 10=15 year age range. This means, belts, hoses, rubber bushings, suspension air bags, etc. This can also include parts in pumps, pressure regulators, etc.