There are so many social media choices for marketing, that it can be challenging to know which is the best avenue for your product. What's the answer? Well it depends.
If your market is 18 to 29 year olds, with average annual incomes of less than $50k, then Instagram is the place to market your products. Higher priced products or services won't do well on that platorm.
If you are a B2B, Linkedin and Linkedin Groups are a good choice, along with Twitter, particularly if you are a service or consulting organization. Both platforms are excellent to help you show your expertise and experience. Twitter is not used as heavily as Facebook, but for those who do use it, they typically use it every day.
More and more, the aged 29 and up consumers are looking to ads on Facebook so that's a good platform for B2C markets. For sheer size, it wins at 1.9 billion worldwide users or 73% of the US Adult population. I'm not convinced it's a great place to sell, but it is a good place to raise brand awareness.
Pinterest is another avenue, particularly if women are a key to your marketing plan or you use photos extensively, such as real estate. It's a perfect place for fashion, retail, and ecommerce.
Youtube is great for ecommerce and product demos.
Google+ is making inroads and interestingly enough, it's mostly men, around age 29, in a technical world. So, if you are selling geek toys or products, then this is a platform just made for you.
The choice you make depends on your product and the audience you want to reach.