While you need to do them all, the best platform for me is still e-mail. If you develop a list of people or businesses who are interested in your product or service they will open your e-mails, even at a rate of 20% to 30% which is what I get and even accept e-mail on a daily basis. However, the key is that you must provide them knowledge on your business not be selling them all the time. If you use social media post expert articles not advertising so people are attracted by the information you provide. Also, you don't need to do your own posts, commenting on posts by others allows you to use their customer base. Let's say an expert in your field has 100,000 followers and you make an intelligent comment about a post they made, their followers will also see your thoughts.