|
AZW3 is not ePub but it is very similar with Amazon leaving out some features and adding in other proprietary features. MOBI is loosely based on the pre-ePub OEBPS specification but MobiPocket added some proprietary features and removed others which Amazon continued doing after they purchased MobiPocket. Compared to ePub/AZW3, it sucks capability wise.
Personally, in testing Kindle Previewer, Send to Kindle (web version) and calibre to convert ePub to azw3, the visual appearance is pretty much the same with any of them on my Paperwhite 4 (the one with the lousiest display...)
I avoid MOBI since it lacks many of the features I prefer such as being able to use % for widths instead of absolute units which means I either need to use a mass of media queries to set sizes or I need to generate different .mobi files for different screen resolutions. Take a look at the css stylesheets in a Vellum generated ebook. One of them is dedicated to close to 200 media queries taking up over a thousand lines.
If you use Kindle Previewer and split the output file into it's azw3 and mobi components (KindleUnpack does this), it's relatively easy to see the differences though for most fiction books, they aren't all that noticeable.
|