I've not yet directed anything, so I can't say for sure, but I've written a lot and it's so much fun! To me, the writing is really the creative bit. Sure, a director needs imagination and needs to have creativity, but the writer is the one who designs and builds the characters, puts them into the situations they find themselves in, makes them say the things they say. I'm sure directing, which I fully intend to start doing soon, will be a lot of fun, but I also expect it'll be extremely difficult. I don't remember the exact quote, but I believe Alfred Hitchcock once said that he didn't like directing movies, he liked the bits before and after, cause that's where the story really gets made.