Water heater, atomospheric vent or power vent?

How many power failures do you have in your region? Where I am at, there are overhead lines, and we have several per year. Get a good hurricane or an ice storm, and you could be without power for several days. The reason I ask this is because an atmospheric vent water heater will still work when the electricity is out, therefore, you can take hot showers. A power vent one is more efficient, BUT will it be worth the headache of not being able to shower if the power is out. If you have a backup generator in your home...problem solved, get the power vent and enjoy the extra efficiency!