I would suggest Kobo. You can easily install Koreader on it. Then when you want to transfer books, start an FTP using your phone’s file manager, and connect to it from your Kobo’s koreader. This is how I transfer files wirelessly from my phone to my Kobo. If you’re worried about the effort or skill it would take to install it, don’t be. It’s as easy as connecting to your computer and running a script.

I’m really curious about all the people who suggest KOReader. The actual reader is basically fine, but do other versions have navigation that isn’t the complete and utter dumpster fire that it is on Android?

Because navigating my library is quite possibly the worst thing I’ve ever experienced. It’s just a file browser and even on a giant 13" screen and presenting the display to the app as having a bunch of real estate, it fits basically no books on the screen. And there’s no way to sort or filter either.

Well, it’s really meant for e-ink devices. Understandably the experience on Android tablets would be sub-par. I often don’t even use the file browser. As my book is downloaded I begin reading, any of my previous books are neatly displayed in the “History”. So the only reason to navigate the file explorer would be for a book I downloaded a while ago but never opened. I just dump all downloaded books (except manga) to one folder anyway, so I wouldn’t be navigating much. If you have all your books organised neatly into different folders on Android and try to navigate to them via Koreader you’ll have a hard time of it. Would be easier to use your file manger and just open with… KoReader.