I had to hunt to find our rig with the diesel option for the generator. This what I had decided that I wanted. It takes about .25 gallons of diesel to run it at half rating. So I figured I could run my diesel gen for over 80 hours solid without ever shutting it down and still have 1/4 tank of diesel left to get somewhere to get more fuel and this is with only a 26 gallon fuel tank and starting with a full tank of fuel. I know there is no way I could get that amount run time from a propane generator.
Someone stated above about the diesel being water cooled, this is true in the bigger gensets but the smaller ones are air cooled also just like a gas or propane one. It does run at a lower RPM compared to the gas or propane so to my untrained ear it sounds like it is not as noisy as the other two.
But all that being said if you have a gas engine then I would want a gas powered one. If diesel engine rig than a diesel generator. I want to keep my propane for the fridge, water heater and stove.
This IMO