Diesel lasts longer, but you should also be polishing the diesel fuel to keep it in good condition, which is another point of failure. When fossil gas is available, it is usually elected as the fuel of choice because this is unnecessary (as the generator is hooked up to gas pipelines, and no storage consideration is required). Propane will last forever in a proper container, but poses more storage risk than diesel.
TLDR Diesel generators where you might be without mains for a while and intend to replenish the fuel with deliveries during the outage, fossil gas for use cases where gas delivery pipelines are available (urban, suburban), propane for offgrid use cases (rural, cell towers, etc) where fuel longevity is a concern.
if you dont have an ICE car, i think id prefer propane over gas? ill likely have the propane tank for a grill anyways
In this context, "gas" is "natural gas" delivered continuously through pipelines directly to your property. Propane is delivered by truck periodically, and stored in tanks on your property. Gasoline and diesel would also be delivered by truck periodically.
I think he is talking about natural gas rather than gasoline/petrol.