PocketBook if you want openness and long runtime (book-replacement), it runs plain Linux.
Kobo/Onyx if you want Android flexibility, with possibility to flash LineageOS/PostmarketOS (though they’re slow for tablet use).
But personally, if you’re not using it to transcript notes (recommendation Remarkable) or want more than merely reading books, i would go with a tablet.
PocketBook if you want openness and long runtime (book-replacement), it runs plain Linux.
Kobo/Onyx if you want Android flexibility, with possibility to flash LineageOS/PostmarketOS (though they’re slow for tablet use).
But personally, if you’re not using it to transcript notes (recommendation Remarkable) or want more than merely reading books, i would go with a tablet.