The cheapest around here is "Quiktrip", which actually is a Tier-I brand. The convenience store has a local distribution center, which I tend to support for local employment -- and the fuel comes from Oklahoma. Seems to be a good company, and cheap to boot (for a fuel supplier).
I prefer citgo over the quicktrip gas but like most I have no conclusive data.
02 Saturn SL
for pics click the link below