I have the Kobo Libra H2O, which I use for English reading. I read library books, kobo daily deals, and sideloaded religious books I can't get through the kobo store. If I REALLY can't get a book I want through those channels, I buy from the kindle store and deDRM it for reading on my kobo.
I use my Paperwhite 3 for Japanese reading - easier dictionary look up, translation function, and I already own a dozen or so Japanese kindle books. However, I really don't like Kindle's software as there are no page turns left in chapter, which my kobo has. (Japanese books also do not come with print page numbers :/)
I really wish I could downsize to one device, but it doesn't seem to be likely, especially as I'd like to keep away from Amazon as much as possible