Just bought an epub today:
... didn't go with B&N because I can't download/sideload without installing special scripts for their website to download the book without a Nook/app.
... didn't buy from Kobo because the book appears to only be available in their kepub format. I can get around that, but I'll avoid that hoop if I can.
... finally went with Google Books because I could download the adobe ascm file and download the epub using ADE. Yay!! Except that after all that ... turns out it's an ePub3.
I give up.