It depends on where your customers are. Each social media platform has it’s strongest attributes, and it attracts people who enjoy the interface. If you are dealing with B2B contacts, Facebook, LinkedIn and Twitter are great. They will each let you interface with your customer as well.
If you start your social media strategy on a blog platform, (we recommend wordpress), you can hit publish and automate your posts to all of your social media sites. You can choose to spend time interacting on the ones you like, and still have your message in front of the people who like each of the sites.
You can also find out some information about the demographics of each of the sites. What is the age of the users, using Facebook ads you can find how how many men vs women are within a radius of a zipcode and craft messages specifically to those users. It would make sense to create a strategy, considering who your target customer is, and who the bridges to those customers will be. That can help you determine what sites may need some more of your attention.
Who is your customer, and what is your favorite site to interact with them?