The answer (annoyingly) is “It depends”. People hate this answer because they want a magic formula, but the reality is that you have to THINK and USE YOUR BRAIN to decide. There is no one answer to this.
This would be like blindly asking “What city should I live in?” or “ What should I be when I grow up?”. It depends.
So, while I can’t give you the answer, I can give you some ideas of how to evaluate this for your business.
Things to consider when choosing which social networks to participate in:
1. Is your audience there? There is no reason to participate in a social network that your target audience isn’t using. Start with this. Don’t beat them, meet them.
2. How can businesses play? Each social network has different rules about how businesses can participate. Start by learning about how businesses can participate in the social network.
3. What do people naturally talk about there? The more organic your efforts are, the better. For example, I may find that my target audience is on a social network, but they aren’t talking about business there. It might be difficult for me to interject a business discussion in a place where people are talking about something else.
4. How can your marketing objectives & goals be met? Each social network has different benefits for businesses. Know what your objectives are and evaluate the social network against its ability to meet your business goals.
5. What will it take to be successful? Finally ask yourself what you need to plan to invest to be successful in the network. Some networks take a lot of time/effort whereas others require less frequency. Some are cluttered and others are open. Determine how much time/effort/money you will need to invest to be successful.
BONUS TIP: Look for case studies from your industry to see how other people are using the social network strategically.