Each social media channel attracts a different type of user, and some may be better for your type of business than others. For instance, consumer brands often reach their audiences on Facebook, while business to business services may get more traction on LinkedIn. Twitter is more of an acquired tastes, but it is obligatory for the press and other writers. I rarely read my Twitter feed without picking up an interesting bit of news I would not have found otherwise.
Readership of my blog increased significantly only after I became more active on social media. After several years of paltry page views of a few hundred a month, my blog traffic grew to over 10,000 pages views per month as my Twitter followers slowly grew over time.
You can track the contribution made by each social channel in your blog analytics. For me, Twitter has made the biggest difference. You can also tie social media activity to sales in Dynamics CRM with ClickDimensions. For instance, ClickDimensions builds social profiles of customer contacts so you can follow them.