Cross reference each actor with a list of the Top 100 films (your list, The National Film Critics list, AFI, just something); how many Top 100 films is each actor in?
Evaluate range; is DeNiro the same character in each of his top movies? No. Does he have good performances across a range of genres? I would say yes.
Subtract points NOT for bad films but BAD performances in BAD films; thus Oldman can't be blamed if JFK gets crushed under the weight of Kevin Costner. His performance as Oswald is terrific.
Tiebreaker? Boxoffice. Possibly Oscars.