There are ways round the "enforced" registrations of both the Kindle Paperwhite and the Kobo Glo/Aura etc. And if you use Calibre as HarryT suggests, you don't need to let yourself be locked into any store, or indeed any format.
There are readers that aren't linked to any bookstore, like those from
Pocketbook,
Onyx Boox, the
Cybook Odysessy,the
ImcoV6L. Generally a little more expensive, not as readily available, and for the most part (IMHO) not as good as the Kindle Paperwhite.