Penn is a master at acting. I would have been happy with whomever won because they all proved to be the most amazing of the year. Penn was right though, there is no "Best" in Acting.
Winner:Sean Penn-Mystic River
Other Nominees:Johnny Depp-Pirates of the Caribbean: The Curse of the Black Pearl
Ben Kingsley-House of Sand and Fog
Jude Law-Cold Mountain
Bill Murray-Lost In Translation
Sean Penn