I agree with you in regards to The Aviator (see my post #14). Having said that, he would not have been my first choice for the part. If you saw Captain America: The First Avenger, Dominic Cooper played Howard Stark, a character loosely based on Hughes, and was very convincing in the role. He'd have made a better Hughes than DiCaprio.
For that matter, Robert Downey, who plays the notional son of Howard Stark in the Iron Man movies, would have also made a better Hughes.