All gas is the same gas. If you follow the truck from the distribution center you will find that the same truck will fill the tanks at an Exxon, Shell, BP, Aomco, Citgo, Valero, Etc...

The ONLY difference between brands is the small amouts of additives that are put in the tanker truck at the distribution center. The additives are approximatly 1-2 quarts for the entire tanker truck.

For me the most important thing is station quality. You want to fill up at a station that sells a lot of fuel. If the fuel is just sitting in the tanks, and the station does not turn it over fast enough, you will get funky stuff growing in it, you will get excessive dirts, you will get water in it. So, any station is good as long as the sell the fuel at a good rate.

Now as far as supporting a brand, I don't uses some brands for personal philosophical reasons, but I know that I might be burning fuel that was processed at one of their plants even if I did not buy it from their "store".