http://www.povonline.com/cols/COL264.htm "Deciding who's the best actor - or even the right actor for a given part, which is not always the best actor - is an utterly subjective decision...and always will be."
-Mark Evanier (writer/producer for a ton of animated shows)
The above link goes into the grim realities of show business. Worth noting in response to people who mistakenly believe that movies are cast based on the "best actor for the part".