Recent purchases have mostly been manga so been getting them from Kobo (high quality while being easy to DeDRM).
I used to buy all my manga from BN. According to my spreadsheet, I've actually spent ~$4K on Nook manga throughout the years.
However, when I started needing a rooted Android tablet in order to acquire DeDRM-able copies of my Nook purchases, that's when I stopped buying from BN.