I had a Nook for a long time, but when it died I decided to get the Kindle e-reader. You can't beat Amazon when it comes to the sheer amount of e-books available for purchase. The thing I like best about Amazon's e-reader selection is how many free and great deals they run every month.
The Kindle wi-fi is a great electronic device. It's small enough to fit into any purse and is sturdy enough that it doesn't break from bouncing around in the bag. It's easy to read in the daylight. I wish it had a backlight so I could read at night. I think my biggest problem with it is that I wish it had a keyboard on it and that it was a touchscreen e-reader. So many devices are touchscreen that it took a while to adjust to the fact that I had to click on some buttons to type instead of the touchscreen keyboard. Otherwise, for a basic e-reader, this Kindle is perfect for hanging out and reading the latest release.