Facebook is still #1, in terms of visits. Then Twitter would be my second choice, and Pinterest my third choice.
I think the best options for Social websites are Facebook, Google +, Twitter and StumbleUpon They are all non follow but if you can get in with the communities you can generate a lot of traffic through them
According to the findings, Facebook drives the most traffic compared to Twitter and LinkedIn, but Twitter generates the most leads. In fact, Twitter achieves a higher conversion rate (2.17%) than the average for all channels combined (1.6%) including organic and paid search. In comparison, LinkedIn and Facebook achieve conversion rates of 0.8% and 0.74% respectively. Courtesy:- Econsultancy