I use Beam Reader. I don't subscribe to any particular format book. I look for epub and pdf. I found a computer app that would remove DRM. If you use an outfit like Booksamillion, they do list the formats for each book.
My problem is I don't bother with the books that Amazon, B&N usually push. Sometimes there is a nonfiction bestseller that is interesting, but usually not.
I do more non-fiction anyway.
The science section and the do it yourself section are wanting.
The latest book I bought was on GIMP. Some of the other books I acquired were long out of print, but still interesting and free from Project Gutenberg.
The Audubon Guides are Android Apps and just as good as any published ones. The bird one is even better since you can get the actual bird song. You don't need a reader.
If you are a recipe collector, there's free stuff all over. You don't need to buy another cookbook if you want something beyond basic how to cook. Most of it is in PDF, but if it isn't most Office programs will write PDF files that you can read on your device.
I realize that I'm not in step with the majority, but I dislike the assumption that I am.
If you like what most like, then have at it and enjoy yourself.