At the moment I'm getting the impression that I might be using Scrivener for the writing of books. Then I use Ulysses for all of my blogging writing. I'll use Ulysses for all other non-book writing activities. Ulysses does have the advantage of export out to EPUB format directly from the iOS version. I have found you cease to be good as my go to application for writing. Whether that be for longer books or for blogging.
Scrivener does have some more organisational tools and I'm inclined to give it a try for the next book I'm going to write.