g+ help increase rankings too...actually even twitter and facebook do, but +1s are faster, if they are humans...if the +1s are spammy it is the contrary, since +1s are from google it is much easier to track them down respect spammy tweets and fb shares/likes
Higher ranking on google would be google + the biggest impact...more visitors to your site though IMO would be facebook...more users on fb
G+ = More Webmasters & Forum Users in proportion to Social Networkers FB = More Webmaster & Forum Users in total but need to pick them out
If you can promote your site through facebook then your site will get good ranking faster cause facebook is very popular than google+.
Google is giving more preference to +1 button but in my view you should not completely ignore facebook. As billions of people are connected with facebook and ratio of Facebook likes are still more than +1. So use both of them Thanks