On my various commutes I have 4 really, others are just not realistic in rush-hour traffic.
Texaco - A4: Generally the cheapest, would be around 5p cheaper than BP, but the pumps were sh!t, so unreliable. Often not giving right pressure or out of service. Price never on board, had to look at the pump. (might do this on way home)
BP - Hatton Cross: Used to be most expensive, but cheaper recently. Pumps reliable. Currently 61.9
Shell - M3 Sunbury. Reliable, but not on my main commute route, means detour. 65.9 currently!
Shell - Fleet area. Need to check their price. *plus this one is not close enough as a commuter filling station.
Not got any supermarkets around here that sell fuel, Asda High Wycombe was brilliant when I did Brackley-London commute.