Some old timers that didn't have the benefit of PBA competition for very long due to being too old when the PBA was inaugurated, certainly merit consideration as the top bowler of all time, such as Andy Veripapa and Bill Lillard.
As far as those that enjoyed PBA success, I would rate "The Machine" (aptly dubbed for his consistency and accuracy) Earl Anthony as the best of all time, due to his superior winning ratio to tournaments bowled (it's not even close), with Walter Ray second, Mark Roth closely behind him in third place, Pete and Dick Weber tied for fourth place, Parker Bohn in fifth place, and Norm Duke tied with Don Johnson for sixth place.
Incidentally, no one was ever more dominant and more feared during his prime years than Mark Roth. During the 1978 season he amassed 8 titles (still a record), and in the following year compiled another 7 titles (second most ever for a season, his record also), for an astounding 15 titles in 2 consecutive seasons, and these feats were accomplished when some of the greatest bowlers of all time were his competition, such as Earl, Don Johnson, Marshall Holman, Dick Ritger, Nelson Burton Jr., etc.
--------------------
Regards,
BowlingWolf