[BitWielder1]

Get one that's quiet.
Make sure it's outdoors when you run it.
If you store it indoors, get one that's not too big to move yourself. You can put wheels on it.
To connect it legally you need an electrician.
You want a toggle switch so that you CAN NOT have the generator and public supply connected at the same time.
Failure to do so could electrocute line workers trying to fix your power out.
There are kits to switch over circuits one by one but I prefer the whole house switch.
They will tell you that you need a huge generator for a whole house, but that's not so.
Just don't turn on everything at once when on backup power.
Electric stove and electric dryer are things to be careful about.

Consider a professionally installed automatic generator that runs on propane.
It's expensive but worth every penny.

[Lazlo in PA]

You want a toggle switch so that you CAN NOT have the generator and public supply connected at the same time.

Or you can be cheap like me and just turn off the main.

[BillGunn]

For folks living in the northeast where a majority of homes are heated with oil, a diesel generator is the best bet. You can easily tap a second line from the tank to power the generator. Diesel and heating oil can be stored long periods of time without spoiling. Consumption with the diesel engine is much more efficient.

[pingman]

There’s a firm in Bangor Maine that will modify your generator’s carb to run as a dual-fuel setup, gas or propane. Central Maine Diesel, I believe.

Other than that, a slow-speed unit will outlast a high RPM unit 10:1.