Currently I would have to say that title belongs to the Nook. Ya, ya…Barnes & Noble tells you it that it just an ebook reader, but it’s running a crippled version of Android that you can root pretty easily.
It’s pretty straightforward, and you can find just about everything you need at nookDevs. Once you are done, you can load multiple ebook readers, including B&N’s android app!
Downside, no camera and no Bluetooth.
Upside, no monthly service fees!
Disclaimer: In case this wasn’t obviously clear, rooting your Nook is not warranty friendly.