I have only used a friends kindle and haven’t seen the Nook. Look and touch the screen on each device. See how it works for you. See if one is easier for you to look at in various lighting conditions, When there is not a clear technical advantage pick the one feels best for you. Kindle 2 will hold about 1500 non-illustrated books and dose not have a SD slot unlike the first kindle witch did have a standard SD slot. At one book a day it will be years before you need more memory.
I love my kindle, I haven’t tried any of the other readers, so I can’t compare. The only down side is that you spend a ton of money on books because it is just so easy. I’ve read 30 books on the Kindle since the middle of February and my husband is beginning to complain.
There are some books that I prefer to read in traditional form, books that I want to skip around in, or books with pictures, or just books that I prefer to own in hard back because their lasting value or my desire to share. It’s hard to share an e-book.