There is a sticky at the beginning of the Class A Motorhomees discussion area. Helps answer your question!
Choosing Gasoline or Diesel Powered? In fact, there are two:
The power equation...Horsepower- Torque -Gear Ratio- Weight.
My personal preference is the diesel. The diesel engine is more efficient in producing power than the gasoline engine. This is due to the higher compression ratio that a diesel can and does run at. How many gas engines do you see in tractor trailers? One I know of is the 534 Ford. But I don't know one RV manufacturer who puts a 534 Ford in a motorhome. If my motorhome has to have gas, I want a 534 Ford in it.