I prefer forum style CMS applications because in addition to the more static and uniform looking pages of a blog style site, you have deeper customization options available. You can add in real-time chat, you can further break down topics or group discussions in an easier and more robust format. As a site administrator, you have even more control over who can see what and who can add information and/or content to which areas of the site. In my experience, I have found forum software to be a better platform for open discussion and information exchange. However, in recent times, I have been toying around with utilizing both in conjunction with each other to produce an even better website for my “community”.
Here is a new forum I installed on my domain just for this project: http://forum.sleepyoasis.com/
Also, no restrictions on creating an account.