How much is a social media share worth? The study by Eventbrite found that, on average, every time an event was shared that resulted in $1.78 in ticket sales. Drilling down into this number shows how valuable different types of share are:
1. Facebook: $2.52.
2. Email: $2.34.
3. LinkedIn: $0.90.
4. Twitter: $0.43.
from here. So for that site (service) Facebook is the best. But here is another issue, that tops Twitter: 7 times better than Facebook (but it is about click through)
P.S. you can see links from social networks (Facebook, Twitter) for any site with Social Links mashup.