Best work Griffith ever din in my huble opinion was a movie called A Face in the Crowd. He is a wanderer during the depression who is discovered as a folksy person of wisdom by the daughter of a radio station owner played by Patricia Neal. She puts him on the radio and he becomes popular and eventually is elected Senator but then changes as he is corrupted by politics.
Tremendous commentary on the political system that is way ahead of its time. Griffith plays a real bastard of a character and really knew how to portray evil.
Others greats in this film are Lee Remick & Walter Mathau.
Here is a link to find out more if anyone is interested.
http://www.imdb.com/title/tt0050371/