A diesel generator would definitely be better on paper, but the costs involved are much higher as those are generally a permanent install. A gasoline generator requires much more maintenance around fuel and the carburetor as gasoline goes bad over time and modern gas/petrol with ethanol in it sucks up water from the air. A propane generator, while it is a bit more annoying to refuel, especially if you upgrade to larger tanks, is perfectly happy to sit for 6-12 months unused and then start right up on the tank of fuel that's been sitting next to it for that time period.

A propane generator is a temporary solution but likely is good enough for most folks who just need to keep the fridge cold and maybe charge cell phones. It's not going to be able to run your house AC or anything, though.