On the road I buy US Oil companies fuel, nothing against Shell and BP.......well yes something against BP, they destroyed my home state's coastline! Both fine fuels but I like to have my money support American companies. The largest is Exxon/Mobil followed by Chevron, Valero, Conoco/Phillips and Marathon so any of those get my money. At home I shop Midnite Oil, a local reseller that provides 93 octane non-ethanol, rumored to be supplied by Valero. We are lucky in Chattanooga, TN to have it as Fifi runs best on non-ethanol as far as feel and a measurable increase in MPG.
I don't really think that gas is any different than top grade oils, these so called "top tier" are all excellent fuel. What concerns me more is the facility dispensing the fuel. Branded stations usually are more responsible as far as maintaining their tanks and water in the tanks. Many convenience stores do not. Most cases of "bad" fuel come from these and the large budget brands. I knew a guy that made a living pumping water from independant dealers. I drive by any place when they are having fuel delivered, it stirs the water that develops in all tanks into the fuel you are pumping. Once the filling stops the water settles back to the bottom. The pickup tube for the gas pumps do not go to the very bottom of the storage tanks so as not to pump water. When it does happen it is because the water level is as high as the pickup tubes. How does that happen? A leaking cap or not tightening it down both allow rainwater to leak into the storage tanks. Also keeping the tanks topped off reduces the condensation that will develop.