No, gas is not gas. There is always - not good - reason, something costs less. It's common sense wisdom, and you can argue it to death, it does not change what it is - common sense WISDOM. And as such, it should be listened to.
Arco, CircleK, AM/PM - all those cheapo brand stations will NOT improve your gas mileage and in long run, will cause harm to your engine, unless you continuously prime their gas with additives like STP or Seafoam.
But then, what is that you are saving by spending more on them?
Also, you have to keep in mind one thing: all modern cars have ECU/ECM that has learning feature built in. As in - it is continuously monitoring data coming from all sensors and continuously adjusting power train operation to optimize it. Hence, if you stick to same gas and even same gas station, you have your power train optimized to its best for that particular set up. Flipping stations only makes it worse.
That needs to be remembered when any components replacements are done on power train, like sensors, air filters, etc. As engine changes its modus operandi and ECU needs to adjust also. Pulling ECU fuse for about 10-15 minutes clears "learned" mode and ECU re-learns new component.
Sticking to same gas station is no more than simple basic planning, which should be diligently done by any mpg conscientious driver.