There are several reasons why I suggested Discourse (Note: I have not yet looked at NodeBB) For one, it's open source. This is pretty much self explanatory.
We already discussed this before in a previous thread and it was suggested that we try out another forum software before committing to it. The NuBits team did this for us with Discourse. We already have people who are very familiar with how it works and can draw from their experience.
Both our communities share many of the same members. This means many people at PeercoinTalk are already familiar with Discourse and are currently using it. Why make them get used to yet another forum software? It seems to have been a success. In fact, the Discourse forum is many times more active than PeercoinTalk. Not only is this due to the excitement Nu has generated, but because it increases user engagement and keeps people far more connected through modern features like notifications, live updating, etc...
Because Nu and Peercoin are partners, we can share resources with each other. For example, the forum assistant bot created by woolly_sammoth can be ported and used to tip Peercoins on the forum itself. I'm sure the Nu team is working on many other forum upgrades that can also be shared with the Peercoin community. If we go with different software, we won't have the benefit of this resource sharing between the two communities. We'll be forced to make everything ourselves and we currently don't have the manpower to do this. Even the Peercoin tipbot on Reddit was setup and is run by the Nu team.
The forum branding can also fit with peercoin.net. Here is just a quick mockup I did. I'd like to see some darker gray in there as well somewhere, but this is just a quick concept to show what I mean. A lot of these categories will also have sub-categories, so don't think this is the final organization of the forum...
Edit: Also note I forgot to include the coin logo in the concept below. It should be there to the left of the text logo.
Full-Size: http://i.imgur.com/01lb5yQ.png
