The problem with storing fuel is that it takes up a lot of room, and storing gasoline in quantity adds risk to your life, especially if done improperly. A bunch of 5 gallon cans of gas in the garage is not a safe thing to do. Diesel is much safer to store as it is not flammable.

NG is also much cheaper to run on than any other commonly available fuel. Many gas generators can be adapted to NG so they could run both ways. In fact many can be adapted to run propane as well so you can have 3 fuels available.

NG is the most reliable of all the utilities. It is not 100%, but it would be fairly easy to envision an event that would destroy your stockpile of gasoline or diesel that would not affect your NG supply.

I do not think there is a perfect answer to the fuel problem with generators.