Though the Nook is quite clearly the superior device, which device you choose should chiefly concern how much money you're willing to spend.
The Nook is more expensive than the Kindle Touch and it doesn't sweeten the pot with the awesome deals that are so easily accessible from Amazon.
Amazon also has the best way to buy books - whether online or from your device. Navigating the Barnes and Noble store can be a bit painful and you might lose interest before you buy a book, whereas on the Kindle you'll constantly be excitedly spending money on books you don't even have time to read.
While there are no easy answers, there are a few givens: the extra $50 Amazon charges for the Kindle Touch with 3G is not worth it. Books are downloaded so rarely, that you hardly even need to be connected to WiFi on a weekly basis.
The right e-reader
If you're apprehensive about even getting an e-reader, get the $79 Kindle. At such a low price, it's easy to spend the money without buyer's remorse and you can find if the value of an e-reader is enough to warrant moving your library digitally.
On the other hand, if you're using an older Kindle or just ready to get a stellar e-reader, we suggest either the Kindle Touch - which is absolutely excellent for navigation, or the Nook Simple Touch with GlowLight.
There is no better reading device than the Nook (that's right, not even a book!), and until Kindle releases its own backlit Kindle, this is the best you can do. Even so, you have a right to be squeamish about a ramshackle navigation system, a lack of Amazon Prime-style free books, and a less-than-inspiring storefront.