[Tarana]

After some testing, even older kindles, such as Keyboard Kindle and K5 work fine with AZW3, so even I am completely switching to AZW3. AZW3 allows some of the newer functions such as greater span of font sizes and bolding at different amounts on newer units.

I do recommend keeping the original epub version until you've actually read a book. Sometimes the conversion isn't quite what you wanted (i.e. lines between paragraphs and no indentation when you wanted no lines between paragraphs and indentation). I have both formats because I still have Nooks which use epub.