I’ve had a few people ask me the question “what is better, making a blog or a forum? It’s a good question if you are looking at it from an SEO point of view. My advice to those people is to start out with a blog because they are easy to set up and free. Once set up all you need to do is advertise and manage the content. The hard part is to be consistent with the blog and keep on top of the content so you rank in the search engines. People tend to get bored on one topic and move onto something different but if you can stay focused then you will be surprised by the amount of visitors coming to your site. A forum on the other hand is also easy to set up especially if you are using a forum software like SMF, Bulletin and Phpbb however getting traffic to a forum can be harder too.
In my experience Blogs tend to get more of an audience which can also have them participating in your blog by allowing them to submit comments which can make the blog into an established information source on any subject you want.