Well, Dr. Iannotti and Dr. Warner work together on books with Dr. Williams for complex shoulder problems. I've had all 3 operate on me (Warner when he was still at the University of Pittsburgh, Iannotti after he left the University of Pennsylvania and arrived at the Cleveland Clinic and Dr. Williams at both UPenn and the Rothman Institute).
They are all excellent, you can't split hairs if you are lucky enough to get one of these 3.
I also had Dr. Bradely (Steelers surgeon) and Dr. Morgan (famous for Curt Schilling's surgeries) but I would return to Iannotti, Williams or Warner without question. A friend did his shoulder and elbow fellowship at UPenn while Iannotti and Williams were together, he basically said if they can't fix you no one can. He is now a prominent shoulder and elbow surgeon in NYC... so if that isn't a ringing endorsement then I never heard one.