Twitter is the best by far, if you know what you are doing you can amass a lot of targeted followers pretty quickly
For me there is not a particular one , there are some which I work on regulary .They are facebook , twitter , eZdia , linkedin , orkut , myspace.
From most of the people I read, Facebook and Twitter is good. Just want to understand what are proper steps to get traffic from these social networks?
LinkedIn is great if you're into Network Marketing and Internet Marketing - I get quite a few leads from LinkedIn. Facebook is a fantastic place to start too.