Reflowable ebooks have the widest distribution opportunity in the marketplace.
Most ebooks are reflowable. Books with black & white text and little or no images are the best candidates for a reflowable epub file type. As an alternative to fixed layout, there are creative ways of designing reflowable digital books for complex titles like cookbooks and art books. Consultation with editors and designers may be required if content needs to be reconfigured—for example, sidebars will need to be anchored to a certain text, or original art may need to be redesigned to work in a single-column configuration.
Also, reflowable ebooks allow the user to search text, change the font style, and change the font size. For these reasons, it's the most common and most preferred file type.