Which Screenwriting Program do You Prefer?

You can not be a first time screenwriter without a program in my opinion. My current gig is revising and rewriting a director's script because it was his first screenplay and had no idea what he was doing while writing his story in Microsoft Word. I write with Movie Magic Screenwriter 6 from Write Brothers, Inc. http://www.write-bros.com/ I do not have a single complaint about this software. It will show you everything you wanted to know about screenwriting and whole lot more information that you didn't even know existed! This is my second screenwriting program from Write Brothers, Inc. and I honestly believe that I will never stray from them. Do you have a favorite?
http://www.write-bros.com/