I will only say what I have experienced between between Murphy USA and Quik-trip. When I used Murphy USA, I would consistently get 22+ mpg. I then switched to Quik-trip and could never get over 20 mpg. I did the same type of driving too.
One time in December I filled up with Murphy USA between two fill-ups at Quik-trip and it averaged 21 mpg, but then I went back to Quik-trip and it went back down to 20 mpg. I switched back to Murphy USA a couple of months later, and mileage went back to 21 mpg on the first fill-up, and the next tanks thereafter were 22+ mpg.
I have since stayed using Murphy USA and even during the winter months, there is no noticeable drop in fuel mileage.