John Colicos as Cromwell
Personally, I think John Colicos' portrayal of Thomas Cromwell is the best on film, bar none.
Wolfe Morris who played the part in The Six Wives of Henry VIII and James Frain who played the part in The Tudors come in a close second, but Colicos has this evil and slimy streak that is the epitome of Thomas Cromwell from all accounts of his personality.
Everytime I see Colicos in another part, I always think of his role as Cromwell and would have loved to have seen him in The Six Wives of Henry VIII playing "Crum" from his rise to his fall from grace.