Most gasoline markets have regulatory requirements for the fuel blend and a detergent/deposit control additive is always required. Most stations in a given geography, regardless of brand, buy fuel from the same local wholesalers, and the slight difference in additive package is blended in the tanker truck.
Bottom line is that most gasolines in a given market are essentially the same, but brands try to differentiate through advertising.
I recall one petroleum industry engineer recommended a strategy of switching brands regularly. This way you get the benefit of all the various additives packages used by the different brandks.