Has anyone tested the effectiveness of social media signals from Twitter, Facebook, and Google+ as applied to influence on search engine rankings? For instance, is it better to have 100 +1's, or 100 Twitter mentions, or 100 Facebook likes?
I've also been curious about this one and decided to analyze the social media stats of some immensely popular domains, such as Mashable and PCMag. What I found (I used the webmeup tool, the social media module) is that they massively target Google+, I guess it's kind of "we want to rank better on Google, so we'll invest more time on building our presence there" vision.
But as a side note, I'd focus on the network that can potentially bring more traffic to your site.