1. John Ridley, 12 Years a Slave
It's a great screenplay, Shakespearean with its screenplay. The dialogue is wonderful, but the pacing is poor. Leading film contender and pretty much a lock for a screenplay win.
2. Terrence Winter, The Wolf of Wall Street
Winter's energy is boundless, contagious, and infectious. Worthy of all its praise, it's one of the film's best aspects, and I'll be surprised if it wasn't nominated.
3. Ethan Hawke, Julie Delpy, Richard Linklater, Before Midnight
No, its not my bias kicking in, the film's screenplay is the one thing that's playing into the Oscars. I wish it was a lock for Best Picture, but hey, beggars can't be choosers!
4. Billy Ray, Captain Phillips
It's going to be nominated. No comment.
5. Steve Coogan and Jeff Pope, Philomena
Other films to consider are The Spectacular Now (oh how I wish it was nominated!), Tracey Letts' August: Osage and even Lone Survivor, which did manage a WGA nom.