I LOVE LOVE LOVE my Kindle. I have no experience with a Nook, so I can't say. I use my Kindle every day and every night. One thing I love about it is that if I get sleepy, I just close it and the next time it opens right up to where I left off. I have the 3G, and when I turn the wireless off, my battery lasts about a month. I can download books with one button, right from my bed at night if I want. Tons of free ones, too. I'm like ssgramma. If mine broke, knock wood, I would immediately buy another one. I can't imagine my life without it.
Hubby had Kindle-envy, so I bought him one for Valentines Day. He loves his, too. My daughter then got one, and her husband soon after drank the Kindle koolaid :) They downloaded books while we were onshore in Jamaica on a cruise!
Amazon makes it waaaay easy to buy books... and when you have Kindle for iPhone and Kindle for PC, they are downloaded to all your devices. I know I sound like I should work for Amazon...but I really love my Kindle.