ARCO for me here in WA and down in CA. Its cheaper; considerably cheaper. ARCO is now part of Britis Petroleum BP. Used to just ARCO, before that ir was Atlantic Richfield, before that Richfield Oil Co. Major oil company with their own stations. Doubt they could provide substandard product for long.

Additive...how much is enough? Enough. Believe the Top Tier gimmick is mostly a marketing deal. This from a pdf at the GM website:

"Why was TOP TIER Detergent Gasoline developed?
TOP TIER Detergent Gasoline was developed to increase the level of detergent additive
in gasoline. The EPA requires that all gasoline sold in the U.S. contain a detergent
additive. However, the requirement is minimal and in many cases, is not sufficient to
keep engines clean. In order to meet TOP TIER Detergent Gasoline standards, a higher
level of detergent is needed than what is required by the EPA. Also, TOP TIER was
developed to give fuel marketers the opportunity to differentiate their product."

Read the last sentence carefully; why do they need to differentiate their product? So they can charge you more for it. Fuel is a commodity like laundry detergent. Sure you can get some stuff at "Dollar Store" that isn't very high quality, but the major brands are all Ok.

As far "the requirement is minimal" well, so what.
If the minimum wasn't good enough it wouldn't be the minimum, and the car companies and consumers would be squawking.

"a higher level of detergent is needed than what is required by the EPA." Yeah, and that's to meet THEIR standard not necessarily what is required to run your car just fine. Where are all of these cars that have sticky valves and preignition due to not using the hyped product of some oil companies. Lot of guys here work in the business; do they see engines with service life reduced because of not running Chevron, Shell, 76, Conoco, etc. etc. Bought a new Toyota last year. I don't recall seeing in the owners manual any recommendations to use only "top tier" fuel.