I use a Kobo Libra 2 and I find it great. It replaced my Paperwhite. It's easy enough to side load apps if you want too (but I find that I don't - I just need it to read books and it does that well)

I have two Clara HD and they’re pretty good. They just work. I use Calibre with them.

Inside is a micro SD card so if I ever need more storage I can just clone the original SD and extend the partition to upgrade the storage.

The Kobo are so much better than the kindle imho: more open, not locked down, and the typesetting engine is Mike’s ahead: no ragged edges or page long rivers unlike I was getting on the kindle.

I picked up a Libra H2O a while back, I've had no issues whatsoever. I used the default software without issue before discovering KOReader, installation was easy. The hardware is very solid, have not noticed any problems with the outside casing, screen, or issues related to power.