I think do follow blogs give good backlinks. Forum signatures can annoy a lot of people in certain niches if those links are viewed as having bad content. Even if they are good links forum signatures seem pushy and spammy on certain forums. I would go for some .edu and .gov's if possible. Articles are a good source of backlinks but require hard work (you have to write articles).
Google are considering all dofollow links as a backlinks & if you are putting your link in high PR then its very good..
In my opinion I will give the marks accordingly. Article submission Press Release Social Bookmarking Commenting Social Networking Forum posting Dir sub Competitor analysis
link building is very important to getting a higher ranking on google, I recommend that you write and submit as many articles and submit to as many directories
I read in some of post that three way link building is also very effective way of link building. Is it ?