For me it depends on the type of book. For anything that is primarily text, I always prefer epub. If I have the option I grab that and use Calibre to convert to

For me it depends on the type of book. For anything that is primarily text, I always prefer epub. If I have the option I grab that and use Calibre to convert to anything else. If the book has a lot of graphics or other content that doesn't translate well to a smaller device (I read the vast majority of books on my kindle, a few on my Galaxy S3) then I prefer pdf. A book I bought on using Gimp falls well into that category. I don't even bother trying to read it on anything less than a 19 inch monitor. There are too many large images and layout is too important. Comics I prefer in PDF or CBR - either way. Though it still falls into the same issue that I haven't found a good experience with comics on my Nexus 7 or anything smaller. They are the only thing that has made me feel the desire to purchase a larger tablet.