Thanks, Zelda.
To clarify, I am not interested in hashing out the DRM is evil argument, nor in the 'I would never ever buy a book with DRM' one either
I am interested in hearing from people who DO BUY BOOKS WITH DRM about what format they choose. eReader has always felt like the most future-proof to me because it decrypts to plain HTML, but it is messy and time-consuming and I lose things like the graphics and layout. I was scared off from epub because it didn't look right in the Calibre viewer, but when I tried loading it onto my device I realized that it was because I was not seeing things like page breaks properly on my computer screen and they looked great on my device. So I am reconsidering.