Propane puts out more BTUs and if you already have propane service it makes a good match, but only with a permanent installation. Propane is more efficient than gas and burns much, much cleaner.
Even though I have propane service, in the end I opted for portability and convenience as it is easy enough to get gas. And our use is limited to power outages only. I got a Generac 15000 watt that can power my whole house with plenty of watts to spare. Unless you are using the generator a lot, gas will be the easier route to go. Much less expensive as well for the generator and the installation.
But it really depends on your needs. If you are going to need a permanent installation and plan on extensive use then go propane. Definitely a more expensive option though.
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.
When we built our home out here in the boonies, we had them install an automatic propane generator. In a power outage, it will run our well, septic system, heat and a lot of the downstairs outlets. It, conveniently, powers the circuits to which our fridge, microwave and coffee maker are connected. Also conveniently, it does NOT power the circuit to which our range is connected, so I don't have to cook "real" meals if the power goes out.
We do have to make sure that we keep our propane tank filled, but we also run our hot water heater and gas fireplace on propane, so we have a 300 gallon tank. Our power was off for a couple of days last year, and that generator saved our bacon - literally. It's also nice because you don't have to worry about refilling it, like a gasoline one.
Whatever you decide, I'd get the biggest generator you can afford - there's always something else you wish you could connect!
The one hubby is looking at operate on a 20 pound portable tank, like what you would use for your BBQ grill. We only want it as a back up to run, say the freezer, should we have an outage lasting more than a few hours and a for a few other appliances. He reasons that it's cheaper. Those tanks are about 20 bucks and wouldn't go bad. We could keep a half dozen of the propane tanks on permanent stand by. And the generator is still portable. We wouldn't anticipate using it all that often at this point. He was all set to get the standard gas powered one till he ran across those propane ones and he's back at square one now, being research! Keep your experiences coming and thanks to those who have replied.
That is the best advice. I've found that if you buy more power than you need--be it a generator, lawn mower or incubator--you're less apt to have buyer's remorse. Better too much than too little.
we have a whole house propane generator. it turns on automatically when the power is out for 10 secs. then shuts itself off when the power comes back on.. since we live in the boonies we use propane for our cooking, waterheater and heating so the tank outside is large. when you use gasoline the generator will run a few hours at best and has to be refilled.. but if you have a major poweroutage the gas station pumps aren't going to be working anyways.. so getting gasoline might prove to be hard to come by. we chose propane just for that reason. we have also shared out power with neighbors to keep their sump pumps running and their freezers and fridges going . ours will run 90% of the sockets in our house so the well and all the important things will be going. a few years ago we had an ice storm and some people were without power for over 2 weeks.. you just never know