Whether email marketing or social media marketing will be better for you largerly depends on what kind of business you are doing, who your customers are and what is the goal of your communication. Email marketing, how old-fashioned it might be labeled by many, is still one of the most effective method of online marketing.
"Email actually drives a lot of the social web activity, through notifications, alerts and more. Email is a great complement to social in that it allows marketers to extend the reach of their messages and identify influencers on their list," says Greg Cangialosi, CEO of email marketing company Blue Sky Factory, which also partners with Mashable.
That being said, however, social media is definitely efficient in spreading the word around. The best way to go about deciding which approach is best for you is to use both. Study your ideal customer and their behavior, learn more about how to make your email marketing more efficient, get to know what works on social media, then test, monitor and analyze.
Hope it helps.