Obviously Facebook.... It is the most interactive and user friendly site filled with lots of features.
Every social signal are not much different from others so I guess G+ will be the number 1 in 2014 it's because Facebook and G+ have stiff competition.
I still use Facebook, G+ and Twitter, but Pinterest is gaining as far as I know. I've been seeing far more picture quotes online lately linking two and from Facebook.
Facebook is still going very strong so Facebook diggdirectory.com | Increase Traffic | submit site | International website directory
The anwser is obviously facebook, however Google + is rising daily and it has a great design. It's just a matter of time that facebook isn't top. Twitter will eventually be No.1 and then 1-2 years after Google+ will take over.
Facebook is becoming much less popular, especially with teens, who account for a large part of social media usage. Teens and TV shows frequently use/promote twitter, which I think could take over.
Facebook will still be the most popular social network around. They've got a HUGE number of users, however in terms of information and sharing I feel like twitter might get some more attention this year. More and more people are starting to use it, and though, compared to facebook, it has a significantly smaller audience, people who use twitter seem to be more influential. It's a first-hand source of information about anything to do with current events, and I feel like that might be very important this year.
I think Pinterest and Instagram are becoming far more popular now. Picture quotes pop up on Facebook from those two places all the time.
Facebook will be a leader by number of users but other social networks can show good results in growth dynamics.