Try to use a gas station that seems to sell a lot of gas. It’s less likely to have any contaminants or water seeping into the holding tank if it is sold as fast as it is put in. That’s my theory anyway.
I’ve always used ARCO in California. The “A” means Alaska (at least I think it does) and Alaska is a source of low sulphur clean oil which refines into excellent clean gasoline that won’t gum things up in the engine , so ARCO is a good choice from this point of view (another unproved theory, I admit). And ARCO has some of the lowest prices (this is pretty much proved). The downside of ARCO is that they prefer you pay in currency. You’ll be charged a little extra if you want to pay by debit card.
I expect the other low price stations have just as good of gas. Valero, Rotten Robbies (in Calif). I think the V in Valero means the gas comes from Venezula instead of Alaska, but that’s just another unproved theory of mine. It’s probably all mixed together no matter where it comes from.
Beyond all these theories of mine, I think the best thing is to use the octane rating you owner’s manual says, then shop by price for gas. There is a wide range of prices charged, even by ARCO stations. There’s a few web sites that track local gasoline prices and tell you where the lowest price ARCO station is.