For the regular stations, keep in mind that all their gas comes from the same pipes. Chevron gas stations may not be selling gas originating from Chevron refineries. No way to tell, it becomes anonymous once it enters the pipeline. Once it reaches distribution points, the different brands add their own brew of additives, and perhaps that is important to you. When I'm looking for a gas station, I try to pick out ones that are new, clean, and look well maintained -- hopefully this means that their tanks are clean and well maintained as well.