I've got a Nexus 7 (tablet) and highly recommend it, tho the battery life could be better. It does have the proprietary Google Play, but I rarely use that, I primarily use the N7 for borrowing books from library and reading, using it as a gps when I'm going somewhere new, flying, sometimes music, etc. I don't have a smart phone, and it can take the place of most every fx you'd find on one.
From what I can tell, you can get an app to read any type of ebook on most of the different devices.
A couple of years ago I had a early version of the Pandigital Novel e-reader that I really liked; it was almost as good as the N7. The one thing it lacked was a camera and being able to download library books directly from the net, although maybe a more knowledgeable person could figure that out. Sad to say, I dropped it, which eventually killed it. The N7 is tougher :-)
Before I chose the Novel, I bought/tried and returned a number of different makes. Takes time but that's the best way to find one you like.