The prices between the two are for the most part identical, and the devices are close enough in specs to each other to make that irrelevant for reading. If reading is the goal I would strongly suggest that whichever one you go with you choose the e-ink readers. I have read on phones and tablets and no matter how you adjust the screen it isn't as nice an experience as reading on e-ink by any means.
Personally I would say to go with the kindle, they have a larger catalog of titles by a very large margin. Also if price of the books is a concern they have an overwhelming amount of books that are offered up as free every day. This is in addition to the old books that now are considered public domain and available for any device, including the Nook. They have hundreds of books at any one time ranging from self published works to books that were distributed in print form at one time that are made free either because the author wants them to be, or for promotion. You will see a lot of first books of series made free in hopes that you buy the rest of the series.
I go into much more detail on the hub I published a while back at https://hubpages.com/literature/More-Free-Kindle-B... and you can see there how to find them easily.