To some degree what you use is dependent upon what type of content it is. Is it purely text? Text and some images/graphics? Tables? Equations? A good starting

To some degree what you use is dependent upon what type of content it is. Is it purely text? Text and some images/graphics? Tables? Equations? A good starting point for primarily text or text+pics is whatever editor you like to use everyday. Once your content is final (or nearly so) you can export as ascii and then add latex (or variant) formatting. If it is heavily equation oriented, there are a number of wysiwyg type latex editors that may be helpful or just bite the bullet and start as a latex text document.