I voted other (forum profiles).
For me, there are just not enough article or website directories that carry enough weight and authority to create many backlinks on. There are, however, a huge amount of forums and I even went as far as creating custom mods and scripts to generate profiles on forums where others simply can't. And the results speak for themselves!
However, I have to add that not all links are created equal. No matter where or how you build your links, you want to make sure that the site you put your link on is of high quality. There are lots of factors Google looks at when determining the value of a link, f.e. if there's the nofollow attribute or not, the PR
value, number of outgoing links on that particular page, if the page is part of an authority domain, the loading and crawl speed and a few more.
Always go for high quality links, not some $10 spam blast from BHW