Whats the best way to get this fitting off

I clean out the inside of the fitting of as much corrosion as possible with a Dremel wire brush, soak in penetrating oil, then use an inside and outside pipe wrench together if it's a stubborn one. Cut and crush as a last resort. I don't like to put a torch on aluminum, but, I necessary keep it to just a propane one. Use some good pipe dope like Never-Seize on the new fitting so you never have to resort to this again.