Here usually the cheapest stations also have the highest volume. Which dictates high turnover, which equals fresh gas. I stay away from low volume stations. They're usually too expensive anyway.
I think this is especially important if you drive a Diesel. Water in Diesel fuel can really cause problems. And NOTHING on a Diesel is cheap to fix. I have heard not to fill up if the tanker is there dumping a load, because it stirs up all the crap in the storage tanks. I don't know if that's true or not. It sounds like it could have some merit.