As per my experience, facebook and Google+ are the best social networking sites to get traffic for the website.

facebook is best to promote a business campare to google +and twitter is also one of the social media site to promote a business

In my opinion, Facebook is the best way to promote your business, since it's easier to use and can get more traffic.
There's posting limitation on Twitter and I'm not sure about Google+.

I would say you must promote your content in all those 3 platforms to get good exposure and traffic

You can promote on all of these platforms quite well, I use each of the three for my business.
Facebook is a largest social network platform so that you will find it more easier to reach large number of people and quick exposure.

All these three sites is good to promote our online business and it help to generate more traffics.

Twitter, Facebook and Google+.