The Best Social Media Platforms For SEO

I saw an interesting poll on SEOmoz.org where they asked what social media platforms netted the best SEO return on investment.  An informal poll, but the results are interesting none the less. Here is the results so far:

Social bookmarking websites, such as StumbleUpon, was the big winner followed by social networking websites and social news websites coming in a close third.  Social Microblogging is just squeaking in a 4th place ranking, but expect this platform to continue to increase as sites like Twitter become more mainstream.