In the 1926 film, George was played by William Powell who'd become a 1930s star in My Man Godfrey, The Great Ziegfeld and The Thin Man.
Who would I have cast as Jay Gatsby? Aaron Eckhart. He could bring the same qualities and have the same edge that movie star Alan Ladd did. Also, he's a mighty fine actor.
In the previous remake, I liked the gravity Sam Waterston brought to the role. If you know him only from HBO's The Newsroom and repeats of Law & Order...yes. Sam Waterston was once a young actor who accompanied Robert Redford as Gatsby.