There are many contenders for the most effective social media too around, and just as many promoters.
“Email marketing” and “Content marketing” usually occupy the first and second places, but to my mind are one and the same. Email does not work without content, and vice versa.
Further down the list you get bombarded with the names of platforms, facebook, Linkedin, Pinterest, et al, then tools and services like SEO, landing page optimisation, affiliate selling, yada, yada, yada.
The one tool we know for sure that maximises the chances of success is a real conversation.
Two people sit down, exchange views and ideas, interact as humans have throughout our history, and determine if there is mutual value in doing business.
Personal communication can be confronting, is extremely resource hungry, hard to schedule, and is still a punt, but perhaps those real hurdles are why it still works best.
The management challenge is to deploy the limited and expensive resources for a return from this most effective of social media investments, your obvious commitment to the other person.