Brands of Gasoline
I realize that each market is different, but most all of the gasoline in the same area will come through just one or two "distribution centers" (where they fill the tanker trucks that deliver the gasoline to the retail stations). These 'tank farms' are supplied via huge underground pipelines that come from the refineries.
Around here, we have BP/Amoco, Shell, Gulf (very few of them, though), Exxon/Mobil, Wawa, Citgo, Sheetz, Love's, Kroger, Costco, Sam's Club/Wal-Mart and a few wayward Sunoco stations. Additionally, there are the "mini-mart" places and the mom & pop convenience stores that sell fuel. Contrast that to just two or three wholesalers and it becomes obvious that different brands of gasoline are likely going to be the same blend.
I have heard that some brands mix in some 'additives' at the station, but I don't know if that is true or just urban legend. If you buy "off brand" gasoline, you are still getting fuel of similar quality as the name brand gasoline....but you just don't know which one it might be.
In VA (at least everywhere I have driven), it is now EPA-mandated that all stations sell E10 (10 percent ethanol & 90 percent gasoline). There are a handful of stations that carry E85, but you must have a "FlexFuel" vehicle in order to use it.....and your fuel mileage will plummet {because of the lower BTU content} more than enough to offset any savings at the pump.
I buy gasoline at different stations - quite often at Sheetz or Wawa - best prices, easy access and the 'pay at the pump' feature where you don't have to give money to an attendant or waste time going inside and waiting in long lines. I know that they are very good about changing the exterior filters on their gas pumps and they sell quite a bit of fuel all around the clock, so it doesn't have time to collect condensation or silt in the underground tanks.
There was an article in our newspaper about the truths and myths regarding gasoline quality. If I can ever find it, I will post a link to it.
P.S. No matter where you get your fuel, I recommend putting in one bottle of super-concentrated fuel injection cleaner after every oil change or every 3,000 miles. I've done that for the past two decades and have never had a problem with my engine getting enough fuel or experiencing a clogged injector.