Facebook still has the volume and it is a good way to promote your website and your blog. Google +1 is still changing its features and attemping to bring in more users. I recently read that Google +1'ing can create good results. So, if you have a +1 and are reading articles, blogs and other items then +1 and grow.
Try not to do what everybody else is doing. If your niche is very visual, why not use Pinterest or Instagram? If you communicate well, why not take advantage of Google + hangouts? If you do what everybody else is doing, you'll just be screaming in a high wind, nobody will notice.
Facebook becouse Facebook is olderone and active users spending hours of hours on this site and Google+ is new still in test mode users are increasing forcly not many active users but it shows hope for bigger
Both Facebook and Google Plus is important for Social Marketing. Not only these two but also every social sites gives you good traffic if you promote your website there. But Now-a-days Facebook is most popular social sites among all.
every social sites have it's own feature which plays an important role in driving traffic and facebook is the most important social media site since it contains plenty of users,and also facebook is the most popular site for social media marketing
As Dani told buth the Social medias are free.
You should try Both, and also try many other like Twitter, likedin etc...
And you should start to share this all with your friends or group.
so that your friends of friends /followers of followers can see your website,
and so this brings a great traffic to your site,
you should share image (graphic image) on fb, Twitter, Google+, etc... so one can wish to enter your site and bring traffic.
Best of Luck !!!