Facebook is the most used and the top social networking site and people are using it widely in the entire world. It is useful not only to make a huge network for friend but one can generate good traffic for the site.
On other hand, Google+ is the social networking site from Google. People are not using Google+ also. Time will tell tell the future of these two social networking sites.
You would say FB has more traffic at this moment? That's an understatement. Google+ claims to have 90 million users, but people only spend about three minutes a month on it.
Facebook, which has over 800 million users, sees usage of six to seven hours a month (this is according to comScore). And I bet that's an understatement as well....I'm sure there's people that use FB that much in a day!