I have a Boox Nova Air which is still going strong after around 2 years, and honestly it’s pretty good for writing. But I heard a lot of people having problems with updates bricking the device or receiving a bad unit and having an hard time returning it, if bought directly from them. I did not have to talk with support and I avoided the updates, so I can’t say more about that. My experience is overall good with it.
I also have a Kobo Libra H2O that I think is nearing the 4 years mark, and is still going really strong. The biggest problem I had was that it asks for a kobo account during setup, thing that I really dislike. I don’t know if it is still like that.
But, generally, if you want an epub compatible reader that you can mod (NickelMenu etc) and easily side load stuff to, with a kobo libra you can’t go wrong. Even if, to be fair, I’m not up to date with the latest devices and company policies.
One note: the kindle format is pretty closed and all the stuff you buy from amazon is generally DRMed to hell, so it’s not certain that you can pass it to other readers. Just avoid amazon’s ebooks.
EDIT: One thing I missed: PDFs on the default kobo software are bad, the Boox default software for PDF is far better and - in my case - there’s a screen size difference too that can make my opinion biased. Aside from that for pure book reading kobo is generally better, but you need to buy a protective case for it: there are a lot of cheap and good quality compatible ones.
Give technitium a go, my woes diminished drastically with that.