With apologies to the Goldman, Brown, and Thomas families, OJ Simpson may be one of the top 3 running backs in the 95 year history of the NFL. He's by far the best running back in Bills history. Thurman Thomas was a better all-around player, but that does not make him the best runner. The only player I'd pick over OJ would be Jim Brown. After OJ and Thurman, its a toss up between Cookie, Cribbs, Travis Henry, Fred Jackson, Marshawn Lynch, but those latter guys are like 10 steps below OJ and Thurman.
Since we're on this topic, it's kinda interesting that the Bills have had the best special teams player (and future HOFer) Tasker, the best DE ever in Bruuuce (Deacon Jones and Reggie White are behind Bruce in my eyes), one of the best RBs ever in OJ? That's pretty good considering we're a sub .500 team over 55 years.