I go to RaceTrac for 93 only ever since I watched a show on Good Morning America which showed a Shell station with a surprise inspection. The inspection showed that the "93" they were selling people was actually just "91.5". I watched it probably 2 months ago. It was owned by an Arab/Indian family in another state out west I believe.
RaceTrac's 93 passed the inspection.
I try to only go to the newest stations too in hopes of having "cleaner" fuel since everything is new.
Heres a link to a test done a few years ago but I don't think it specifically names stations.
Is Your Gas Station Ripping You Off? - ABC News