What brings in better traffic? A blog, a forum or a wiki? A wiki, anyone can edit. A forum, anyone can post and by doing so make off-topic content which may or may not help your search rankings. A blog, only you and a select few others may add posts, however people can still leave comments if you have them enabled. So out of a blog, a forum or a wiki, which one have you found to bring in the most traffic?
Well, it really depends on the popularity of the topic. And technically, either one of them could get more traffic than the other depending on how successful they turn out to be. I'd say you should create the one that would interest you the most. Wiki is good, but might require more time due to possible spam. As for a blog, you have to be committed to posting often. And as for a forum, you have to make sure your users are happy and keep them active, so it requires work too.
I completely agree. There is no set answer which says all forums get more traffic than blogs. If that were the case everyone would have a forum...which kind of seems the case these days I would go with either a blog or forum. It all comes down to the topic, marketing, and how much time you are willing to put into it. Each can be great, and they both have their plus's and minus's.