I know. This is not a new topic. People have been debating since Google+ launched. I have FB account & visit everyday, I also have Google+, but rarely look at it sine only one friend using it, who is my Fiance?!
My two cents of comparison---
Facebook: 800 millions
Google+: 40 millions (given it only launched 2nd half 2011, this performance has been amazing)
Facebook: Equally distributed, Male 51%, Female 49%
Google+: Male skewed, Male 71% (I bet they are all someone a bit geeky like my fiance), Female 29%