Assuming you're asking about the Nexus 7, I'd say it's probably one of the best 7" devices on the market right now. It's blazing fast and the only feature it lacks is an SD card slot, but with an OTG cable (which only costs a couple bucks) you can plug in all manner of USB devices; flash drives, portable hard drives, SD card readers, keyboards, mice, 3G modems, you name it.
Given the cost it actually blows all of the tablet-style ereaders out of the water. You can easily grab the Kobo app, the Kindle app, the Google Books app and any number of brilliant third party reader apps.
I'd steer clear of the Nook, Playbook or the Arc. All three are too specialized and come with no real advantages over a proper open use device like the Nexus 7.