All share the same hassles to some extent or another. They have to
be run, UNDER LOAD, an hour+ per month. They need the oil changed.
They need clean fuel; #2 Diesel tends to grow weird bugs that clog
the filters. The propane and natural gas can feed modified gasoline
piston engines and turbines. Some Diesels run on a fix of #2 and
gases. [The ultimate example -- a sewage plant will recover sewer
gas and use it w/Diesel. If your userbase is full of BS; or your
tie curls and your boss has 2 horns, you might go this route...]
Natural gas has advantages of no storage hassles; propane does
not go stale.
In earthquake country, natural gas is as prone to interruption as any other
utility. The utility companies actually have shut off valves in the lines
which shut off gas mains when seismic activity over a certain level is
detected. Being as how gas lines themselves are prone to shearing fractures
in the seismic event itself, natural gas doesn't buy you much as a backup
fuel. Unless, you maintain your own tank, which takes you back to most of
the problems noted above.