LP genset are great for convenience use. I use my genset for lunch stops. Hot weather over nights or when ever I need instant electric. With an onboard there is nothing to set up . Just push the start button and your on.
LP is great because it burns clean and doesn't gunk up things however LP has less energy per gallon than gasoline.
LP gensets consume lots of propane.
If you are mainly a convenience user LP is the way to go. If you need to run your genset for hours and days at a time on a regular basis gas is a better option. For the most part diesel does not enter the picture for a towable RV