Glad Escargot had a comparison OP asked for, as someone who had owned both types of Class Bs. I haven't owned a gasser, only a diesel.
Like Escargot and Davyyd, I like the long range on one fill-up resulting from the good mileage. On three two-month trips, including in the Rockies last summer, our mileage averaged around 23 (we have an earlier generation Sprinter.) Has been improving gradually, and lately at 75,000+ miles on the engine, we've been seeing around 25.
We're not heavy generator users, only 5 - 10 hours on a typical two-month trip, so the propane refills have never been a concern.