As other great and brave minds already said:
Absolutely no methanol cut fuels. It's just pure acid under combustion.
Ethanol fuels or whatever your generator can run strongly on... do it.
When storage time comes? Drop the fuel. Run it dry. Pour off that ethanol cut fuel into a frequently used mower or car. Just don't let it sit. Let her sputter out and draw down the tank and carb bowl.
Every season or 50hrs operating ... change the oil. No questions asked.
If you cannot store ethanol free fuel with stabilizer (only really good for 6 months anyway) Go ahead and run the generator on 10% ethanol or reformulated fuel but simply don't let it sit in the generator tank and carbs more than a month. Again simply tilt it over and spill it out and run it dry and used the reclaimed fuel in a frequently used mower or car. The sad truth is ethanol blended gas doesn't age well in any Carburetor or standby situation.
Pure fuels are more expensive. (I.e. Sunoco EtOH free 90 octane premium) But they store easier and last as long as a year with the simplest, cheapest stabilizer additive) *not a sponsor*
Be it on your head that you decide to store mass quantities of fuel or slug it out at the pumps when disaster decides to blow thorough and you simply need it.
Where I live? I'm no bad boy. But when storm season strikes and folks start to get testy for ice, drinking water, fuel and batteries? I keep my 10mm hand blaster in the center console. Stuff gets ugly real quick, yo.