+1 for Kobo.
I've had my Kobo Clara HD for almost 8 years and I still use it daily with KOReader. It's so easy to install KOReader and it's really repairable. I replaced the SD card at one point, and another time I thought it was broken or needed a new battery but came back to life after reseating cables.
Before that I had a kindle and you had to jump through a lot of hoops to install KOreader, and I remember you had to be careful not to upgrade the firmware so it could be jailbroken.
Like I said I've had the Kobo for 8 years, so I hope this is still the case.
KOReader works just as easily, and just as well, on my much newer Kobo Clara BW. I'm not unhappy with the built-in reader software, but keep KOReader installed just in case I want or need it.