I've got a Kobo Libra2.

Pretty happy with the build quality and screen. Less happy with the walled garden approach that Kobo seem to be operating.

That'll probably be something I take into account when I come to get my next model.

Kobo Clara HD. Pretty old now (I bought it in 2018), but it still got updates. I'm very satisfied with it (well I've not tested any other). Perhaps the only drawback if I had to change would be to have some kind of physical button to turn pages, but with the configuration options that it have it's really not necessary.

I have Kobo Forma. Got a refurbished one pretty cheap. Amazing for both books and manga, one of the best purchases I've ever made honestly. Used to have Kobo Glo but the screen was too small for manga, otherwise a very nice compact book reader.

I'm using an ancient Nexus tablet with the Android app "MoonReader" (one of the only apps I have paid for); I would prefer a different setup, to use a FOSS app or not use a tablet, but most physical ereaders seem to have issues with PDFs, no?

I would want something I can just load files on (no walled garden); I currently use syncthing to transfer books to my tablet.