I go to Sunoco or Shell if I have the choice. I've heard some people say that the higher ethanol content in Sunoco 94 is a problem for high performance engines. I'm not sure whether that's true or not, or even whether Sunoco does have higher ethanol than Shell 91.
2015 F82 M4, Alpine White / Black
2012 E92 M3 ZCP, Alpine White / Black, M-DCT - RIP
2008 E92 M3 Silverstone / Black, 6 speed, ZCP wheels, Dinan exhaust, software, airbox & Stage 1 suspension - SOLD
2002 E46 M3 Carbon Black / Imola Red, 6 speed, 19s - SOLD