Has to be facebook from your list of options. But how about stumbleupon? If you have some awesome content that people would share, then this can bring in 1000s of extra visitors.
It depends really on who you're trying to reach. If it's B2B marketing, then Linkedin and Google+ are the one's you're after. But if it's B2C then facebook, twitter, pinterest, stumbleupon, tumblr are the best ones. Ellie, Online Marketing Executive at Sedna LED Ltd
Generally it really depends on your target market but I can say that Google + is the most flexible and Facebook have more active users. So it's more possible that you can increase brand awareness if you are going to market your product to Facebook.