IMO you can never go wrong with a CNET Review:
Kindle Fire: http://reviews.cnet.com/tablets/amaz...-35022491.html
Nook Tablet: http://reviews.cnet.com/tablets/barn...-35059751.html
Fire vs Nook: http://reviews.cnet.com/8301-19736_7...how-to-choose/
Here's my take from the reviews:
The Nook costs $50 (a third of the cost of the Kindle Fire) more.
For that $50 you get a room for expanded storage, more RAM, fancy case design, a few extra hardware buttons (volume and home), better battery life, and a better looking screen (even though they are the same size and resolution).
In other words, the Nook is the better tablet, but you have to pay for the extra features. If they were the same price it would be a no brainer, but if money is tight and your on a budget, the Fire is a viable solution.
Check the reviews and you can make a better informed decision about which one you want.