I'm with Peck Johnson, we have a gasoline generator that runs all of our important house electricity--pump, furnace, refrigerator, coffee maker and some lights--although we also have a propane service.  My reasoning being that I can refuel this generator but would have to rely on getting a the propane dealer here if the tank went dry.  We are at the end of the power line so often have outages when other places don't and ours may last longer.  I try to keep 10 - 20 gallons of gasoline around which would last for 4 or 5 days if necessary although 3 days is the longest we've ever been without power. Even then I could get out to a working gas station to resupply if needed.   I suppose if I were to have an automatic, standby system it would have to be propane but mine is manual start.  I can also service it easily too--mainly just change the oil.