There is mobi7 (.mobi) and mobi8/KF8 (.azw3)
AZW is a renamed .mobi, Amazon does this to indicate it came from their server.
The KF8 is a newer version, more like an EPUB in a database wrapper, and supports embedded fonts and a wider range of HTML.
Also, it handles hyphenated words better, and supports cover metadata so calibre can update the cover without a reconversion.
Definitely go with AZW3.
You thought you could avoid me?
