Here's an update about the current situation.

While we understand that vBulletin is probably the better choice of all three options (next to phpbb, smf), we also have to take the price into account. 140 euro may not seem like a lot of money, for a site such as PGD which currenty has inactivity issues we cant really be sure if its worth it on the long term. So for the moment we're going to focus on either phpbb and SMF, where the latter has our preference. We already have set up a test site to see what its capabilities are regarding a portal and wiki extension.

That said, vbulletin is not completely out of the picture. In the end it only is a cost issue. If enough people are willing to make a donation we can still take that route. I've set up a poll here, where people can submit if they are willing to make a donation, or alternatively choose to go with whatever forums software we decide upon.