Hokie presentation (video of a "prize fight"), but
here is a CNET comparison of the Kindle Fire v Nook HD's. (Note, both are now lower in price than what is mentioned in the video.)
The downside for the Nook - being taken off the market. But the way I figure it is that both the Kindle and the Nook will break down eventually. At that time, since the Nook is currently a generic Android using Chrome as its browser, I can just transfer anything that I need to its replacement (except perhaps to a Kindle - not sure). When the Kindle breaks down, since they use proprietary Android apps, am I locked in to a new Kindle? (Not sure.) (Further note - apparently you can turn Kindle into something that can use all Android apps if you "side load" them. Good for techies.)
In any case, as is, the Nook has more pixels per screen, slightly faster processor, and a slot for micro SD cards.
One advantage often cited for Kindle is that it works well with Amazon Prime. That is $79 a year. I wouldn't want to actually use it as my credit card in that I currently get 1%-3% cash mack on my purchases using my existing credit cards. (Am I missing something. I don't see anything on the Amazon promo page for Amazon Prime promising cash back.) Free shipping is $25 with B&N. Free movies? Maybe. But for the $54 dollars a year, I can get 18 movies off of Google Play.
Per usual, analysis will vary depending upon individual circumstances.