Reflowable layout format is always better than fixed-layout in an online book publishing as it helps the texts and the visuals to take their shape to fit the reading device’s screen naturally.  Reflowable ePub is supported by all major reading devices, unlike fixed eBook layout. https://www.one-read.com/blog/fixed-layout-vs-reflowable-epub-which-format-is-right-for-ebook/