My view would be: 1. Websites would earn you the most. 2. Blogs will earn you the second best as there are many repeat visitors. 3. Forums will earn you the least as the repeat visitors are too much and they sort of get ad blind. But this is from adsense/advertising networks. But if you can regularly find a good sort of deals for your forum (or even blog) regular visitors, they convert the best, because they somewhat believe in what you say on your blog/forum.
i do not agree. for the same amount of traffic, a blog or a site will earn more than a forum. forums have low CTR and everyone knows it/experienced it.
In my opinion HTML site will work more bette than the others WHY? *-You will have the complete control in your ads placement and you will be able to get more and more revenue BUT the problem that you must do a very very huge effort to make your site a Search Engine Optimization (SEO) for your site. Although Blogger and WordPress make most of it Automaticaly......