Astak EZ-Reader Pocket Pro has some problems with mobi files... the tops of italic letters are consistently cut off. And while it claims to support html, txt, and doc, it lies; it sort of displays those, but they're all unreadable. It adds hyphens in places that shouldn't have them, and breaks words in the middle to switch lines and pages. (Sometimes with, sometimes without adding a hyphen.) I had the same problem the couple of times I tried to read fb2; I can't remember if it had decent support for lit or PalmDOC pdb. (I remember hearing it had problems with lit.)
No idea how the Jetbook and Libre deal with those issues.