More power in a diesel? Well, one horsepower is one horsepower, whether generated by a gas engine, diesel or electric motor. But diesels run at higher compression ratios and so are able to generate more power from a given amount of fuel. And they generate it at lower RPMs than a gas engine, so most people feel like there is more power available to them. And diesels come in larger sizes than stock gas engines, so if you need 500 HP to move the rig, diesel is the way to go. But if 300-350 HP will do, you have the option of gas or diesel.
Diesels are much more expensive to purchase and somewhat more expensive to maintain over time. Several filters to replace, 3-4 times as much oil to change, that sort of thing. You can buy a lot of fuel with the cost savings on a gas engine.
One big plus of a diesel powered motorhome traditionally has been that most of them are rear-engine, which puts the engine and transmission noise behind you. However, There is now a front engine diesel (FRED) Rv chassis available and Workhorse has just introduced a chassis that has a rear gas engine as one of its configurations, so the choices have gotten wider.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC