We recommend "add this".

https://www.addthis.com/get/follow#.UkmpRhSOapY

Before you get started, you need to think about if you want a "follow" button or a "share" button on your web pages.   We prefer "share" because this way people can tell their friends about your blog.  The "follow" button allows people to follow your Facebook Page.  You will get more traffic from the "share" buttons on Add this.  https://www.addthis.com/get/sharing#.UkmpmhSOapY

And they already have it designed for WordPress, Joomla or Drupal which makes it easy to install.  They have step-by-step instructions on how to install.