Looks great for the price. As to which will be more popular, obviously the Kindle Fire will win there. No contest.
The Nook Tablet does look better from a price/performance/features perspective. Given that Android isn't as good as iOS when it comes to resource usage the bump to 1GB of RAM should be noticeable, and having 16GB of onboard flash storage plus the ability to extend that to 48GB (actual usable space would be around 45GB, I'd reckon) is a huge plus. If the screen is better, that's another plus. Something I haven't seen being mentioned here is battery life, but the specs I read quoted ~11.5 hour battery life; Amazon quotes 8 hours. If those are true then that's a significant difference.
As to content and what not, there's significantly more people that are in the Amazon music/video ecosystem than those that are into B&N's e-books ecosystem, and I'm sure you could get the format B&N uses to work on the Kindle. More noteworthy is that while these are content consumption devices, they're mainly aimed at media like videos, photos, and web browsing, so most people would still go for the Fire. Other people have also mentioned the $50 cheaper price tag. Which one is the best choice will depend on the person, but however stupid it may sound I'm really put off by the Nook Tablet's silver/grey exterior and bezel/wasted space. It looks cheap, even if it feels good. They should release a graphite or black version at least.