For Gas only, Superamerica. Why? Top Tier, and for the octane rating, seems to provide the beat Octane Adjustment Ratio in my Ecoboost F150 per data from Torque, and when I'm towing, I get 10 cents of gallon on Premium using their rewards card. The downside is most of their stations are starting to feel pretty run down...
After that, Kwik Trip or Holiday for Gas and Convenience Store, particularly Kwik Trip if Food is needed.
Shell generally gives good Octane for the fuel bought but the stations are all independent, so its like a box of chocolates - the good ones are nice, and the bad ones, shudder...
BP stations are a dying breed in Minnesota. Amazing to see what has become of what was once a pretty large network in the state going back to the Amoco days...
The reality is I haven't ever gotten what I'd call bad gas, just certain pieces of equipment that seem to like gas from one place or another (and yes, I know the story that all gas comes from the same place, except when it doesn't, like this area with two refineries with strong ties to certain brands...)