I absolutely hate any format that is not a pdf file. It puts way too much limitation on the content. Just as an example: I use three "systems" most of the time, one windows, one ubuntu, one android tablet. Pdf works with each one out of the box, I can hight text or copy/past it, edit them, heck even open them in some graphic editing software and extract illustrations as vectors, save it in different formats. In contrast to that, for epub/mobi I don't even know what their native editing tool is so I can convert them into pdfs.