[GeoffR]

These are the advantages of each format that I notice:


KePub (sideloaded):

* Quicker to respond to page turn gestures (especially tap gesture)
* Faster text selection (e.g. when highlighting large areas of text)
* Support for footnote previews
* Can double-tap to zoom images


ePub:

* Better hyphenation (kepub reader can hyphenate words in the wrong place if they have trailing punctuation)
* Full justification works properly (kepub reader doesn't properly justify some lines that contain certain common characters such as elipsis and mdash)
* Better support for embedded fonts
* Full-screen mode works without fonts being cut off
* Better word spacing when using full justification

(Apart from the last, all of these ePub advantages are due to bugs in the KePub reader.)