Wallcraft always give solid advice so I'd listen to him.
All I can add is every DRM except for eReader will require you to register with a Windows PC. You capture the information you need like a PID for mobi, ineptkey for Adobe, key from LIT and you can liberate your books.
The one advantage with MOBI is that it is the best supported. And the Kindle for PC works great on Linux under wine. You will be able to also read Mobi books with the Kindle App.