There are a few different eBook formats, and it really depends on what you want to use the eBook for as to which format is better. If you want to read the eBook on a device like a Kindle or Nook, then you would want to use a format that is compatible with those devices, such as MOBI or EPUB. If you just want to read the eBook on your computer, then almost any format will work, such as PDF or TXT.