I go the cheaper route with my genny.
Presently using Syntec 5w-40 bought on close out at Wally World for $1.75.
In the past I have used Exxon 30w Superflow, Havoline Ursa 30w, and Havoline 30w HD. All have served me well, readily available, and affordable.
Hurricanes Katrina and Rita, days...