It all comes down to form factor and features you want. For reading, I prefer the Nexus 7 because it's smaller, lighter and easier to operate single-handedly. Keep in mind, though, while the Nexus 7 might support USB flash drives via USB OTG after rooting, it's a major hassle to have something hanging off your device while you're using it. If you need lots of storage, a device with a built-in expansion slot provides a more elegant solution.
By the way, I ended up buying a Nexus 7 look-alike Chinese tablet since I found the lack of microSD slot on the Nexus 7 too limiting for my usage. Alas, CPU+GPU is no good for gaming and it's missing a slew of features such as bluetooth, GPS, NFC, etc.
