For writing a book, depending on what kind of book it is, you may just want something that is fast and non-intrucive to your typing, using anything beyond a fast and simple text editor can cause too much distraction. I am most comfortable using vim, but just use whatever text editor you find comfortable and don't worry about layout, just the text and the arrangement.
When you are done writing the book, you import your text into something that can take care of the layout for you. Ask your book press company what formats they accept, and pick your tools accordingly.
