[turbo23dog]

Chevron, Sunoco then Shell, in that order preference.

One thing I always figure is that it may not be the brand of gas, but maybe the station itself that might affect my perceptions of the gas I'm getting. If the business looks like its been in the same location for a long time, like 20 years plus or so, I may steer clear of it because I worry that the underground tanks might be old and have more contaminates that a newer station might.

No science behind this, its just my opinion. I have a newer Chevron station near my office and I'll use that one for the majority of my fill ups. Outside my immediate area, then its whatever I can find.