Another option to consider would be a Wiki. Either a forum or a wiki will require a lot of moderation on your part.

I've used both methods. The downside to building your own pages is you're the only one that can post or reply. With the forums, over time, others can answer questions too, and it's more interactive (you can converse back-and-forth). I guess it comes down to your needs more than just which one is better from an SEO standpoint. Both can be optimized for SEO...

On my largest site I'm actively using both methods. I have a section of the site with "evergreen" type articles that will apply for at least a few years, possibly longer. Those are the nice meaty articles that search engines love. I only add maybe 2-3 articles per month now though. I added forums after that and that's a good way to get people coming back and actually interacting more.

Now that I think about it, do both. Use good pages of content (static) for "evergreen" type articles to help get people there and let them ask questions in the forums. In some cases I took really good quality articles from the forums and converted them to static articles so I was sure it would be better indexed. No need to choose... :-)

Forum building is as difficult as knocking together a good content site, but once you get it running will provide, in general, nice fresh content and loyalty. I've done both over the years and find much to recommend and little to detract from using either or both... as long as you're ready to put in the time and effort to get 'er done!

A few months ago I added a forum to an information type website I run. I would receive inquiries almost daily and now I can answer them within the forums. Due to the topic of the website I will never be able to build a community where other people will answer questions. I don't mind answering the questions myself though, especially that new content is added daily as a result.

In those cases you don't even need a forum. Just enable comments on your articles and address the issues there.

We have an informational site and are going to be adding a forum. We thought about comments on every page but then that won't build the interaction we want. So we are going to have a forum topic per page of our website. We are going to pre moderate at first - we may put of people initially but its important that the content is good and can be trusted.