I remember George Saimes who was good (and you just made me remember Hagood Clarke the strong safety) and had the benefit of playing on probably the best defense in Bills' history (McDole, Sestack, Dunaway, Tom "Tippy" Day on the DL - Stratton, Jacobs, Tracey LBs - Butch Byrd, Booker Edgerson, Clarke and Saimes DBs).
But for my money Tony Greene is the best free safety of all time for the Bills. I remember a game against the Jets, he had been injured, but at a crucial time in the game he went out on the field and because of his presence Namath called a time out. There was no play clock back then.
Greene ranks number 2 in Bills history in interceptions and interception return yards and he holds the record for the longest interception return in Bills history, 101-yards. He's 3rd in fumble recoveries, he was a real ball hawk!