Personally I use a Kobo Libra, as it supports sideloading books manually, supports various formats (epub, pdf, etc), has a nice backlit e-ink display, and physical buttons for page turns in addition to the touch screen.

Also doesn't support Amazon, which is always a plus. Nice bit of kit.

I use a mix. Sometimes, I'll read stuff in the foliate app on Linux from my desktop outputting onto a big screen tv.

But I also do an old kindle while lounging on couch/bed and Librera reader on phone (android/f-droid) when I'm on the shitter.

For the most part, I load different things on each and just jump back and forth between several stories. Keeps things interesting and no need to sync bookmarks and whatnot.

Pocketbook e-reader

Boox e-reader. I’m able to just log in to my Calibre web server and download the book right onto my device.

I send them to my kindle. Shameful, I know, but it's what I got

I use the Books app from a downloaded file on iOS