I also have a kindle (3G and wi-fi). I love everything about it. I download books from Amazon and can download also to my smartphone. I have compared my Kindle to the Nook and I am sure that I have made the right decision. I don't have the color that the Nook has, but I do not need color to read a book. The main reason for getting a Kindle in the first place was that with my maturing eyes, I could not read a "real book" for very long, but with the size adjustment for the fonts, I have no problem.
Get online and read what other people say in the FAQs for both Kindle and the others. That makes for a great comparison.