I haven't got either yet unfortunately
However a mate who installs them swears buy the diesel heater especially if doing a lot of free camping, has all your other stuff fridge stove hot water etc uses the gas, he however no longer installs the cheaper one's as there's to many problems getting parts and warranty.
My thinking is gas because you already have the fuel source and no need for the extra tank, also what about I'm the warmer months when you don't use it, any diesel left in the tank can go off
If you have a motorhome that's a different story, you have both fuel sources available so I guess it comes back to personal preference.
I'm some cases now diesel is being used for both water heating vehicle heating and cooking