The e-book market is rapidly expanding. Amazon, Apple, and other online retailers have begun selling e-books to the point that e-book sales surpassed physical book sales in Spring 2011.

Clearly, the future of the printed word is in e-books. Not only are e-books wildly popular, but so too are the readers used to read them. There are two main choices on the market right now: the Amazon Kindle, the Barnes & Noble Nook, and the Apple iPad. All three of these are meant for different types of readers. Which one is right for you?

Amazon Kindle

The Amazon Kindle is the most popular e-book reader on the market at the moment. The Kindle, like the Barnes & Noble milk, uses eInk technology. eInk technology can be likened to Etch-a-Sketch. When you turn a page, the screen refreshes and the Etch-a-Sketch changes text. While this is clearly of a facile way of describing the intensely complicated technology behind eInk, it is essentially the conceptual model.

eInk is intended to be just as readable as printed text on a page. This is in stark contrast to computer screens, which cannot portray text nearly as well as eInk in conditions such as bright sunlight, and can cause eyestrain after many consecutive hours. As a result, the Amazon Kindle is much more comfortable to read for long periods at a time there and devices such as the iPad or a computer screen.

Additionally, the Amazon Kindle provides access to the incredibly large database of books on Amazon.com. Amazon has invested a lot of money and resources into their large library of books online, and it shows. Just about any title that you want to be found on Amazon online bookstore (and they have an option to request a book from a publisher).

For the integrated ecosystem, E ink technology, and a light form factor, most users who want to read e-books should choose the Amazon Kindle.

Barnes & Noble nook

The Barnes & Noble nook was, up until Spring 2011, simply a knock off of the Amazon Kindle. However, with the latest model (released in May 2011), Barnes & Noble has introduced a touch screen to the Nook. The touchscreen uses infrared sensors on an XY axis to detect where the user's fingers are. This means that the Nook does not have a physical keyboard; it is solely a screen for reading. Barnes & Noble's online library of the books is not nearly as complete as Amazon library is, but the nook is worth trying (at any Barnes & Noble store) simply for the touch screen.

For users who do not like the eyesore of a physical keyboard on the Amazon Kindle, is worth trying the Barnes & Noble Nook's user interface.

Although most e-book users should probably buy a Kindle, the Nook is quickly becoming a sound competitor. Who knows? Maybe eventually, the Barnes & Noble Nook (or another e-book reader) will become a strong competitor to the Amazon Kindle in such a way that the Kindle's marketshare is vastly reduced.

Notes: if your prime purpose is to read e-books, do not buy an iPad for that. Its screen is more like a computer screen than a book screen, and it is not ideal for reading books.