Shell Fuel Rewards card is the best program I have found. Five cents every gallon plus ten cents from using linked credit cards at restaurants or grocery stores. It stacks up so if there's been a bunch of linked spending I have gotten gas for a few cents a gallon. Get .20 -.50 discounts often. It does have the disadvantage of a 20 gallon per transaction limit which is a PITA for a motorhome.
That's in addition to the 5.25% cash back on the Bank of America credit card we pay with.
And Shell is pretty much coast to coast. We buy whatever is cheaper, Shell, Wal-Mart, Costco, or whatever. Use the GS card at FJ too. It's good to have options.