I would not waster time on others and focus only on facebook, twitter and pinterest. Then to some extent Google +.
The best social media sites are,Facebook,Twitter, Pinterest, Google Plus, Stubmleupon, Scoop it ,Delicious, Diigo, YouTube, Vimeo .
It depends in the topic for which you are marketing. As LinkedIn is best for business and profession. If the user wants to market some product, then Instagram, is top best site, then comes Facebook, Twitter, Pinterest.
The most popular social media sites which are helpful in increasing traffic are Facebook,Twitter, Pinterest, Google Plus, Stubmleupon, Scoop it, tumblr, reddit, Delicious, Diigo, YouTube, Vimeo, Dailymotion .