Anyone know which are the best gas stations around the chicagoland area? I'm talking based on facts, please none of "I go here cause the gas smells better."

I've heard that Shell, Phillips66 had a good amount of detergents, but as far as good quality gas I'm not too sure.

I really only go to BP Amoco or Shell. Haven't had any problems with them in the past (with different cars) so I stick with them.