I’ve got a kindle keyboard 3 and want to know if there’s anything better out now. My main requirement is being able to load in my own content and have a nice cover/case
I don’t care about apps or web browsers, but it would be nice to have something that is easy to sync or upload data to.
I've been seeing a lot of good stuff about PocketBook. They support all major ebook formats. They're also good if you're privacy focused, though it comes at a price. Their privacy policy makes them the only brand I'd ever consider. Here's a few links depending on your needs and budget:
Basic Lux 4 has a 6" monochrome display. This is their cheapest option.
InkPad lite is their biggest display at 9.7". An all-around solid, affordable option from them.
Era is a 7" monochrome display. I'm drawn to this one due to the functional bezel.
InkPad color 2 is a 7.8" color display. One of their most expensive options.
I already mentioned this elsewhere, but if you're concerned about privacy, you might consider Kobo as well; you can use their readers without having a Kobo account at all. That removes the store of course, but as long as you're ok with side loading your books, you're good.