One of the key tenets of the Curve is that you use free to find an audience and earn the right to talk to them again. A content marketing strategy that just finds an audience with no follow-through is not a strategy.
My preference is email, because it is in my control, but it is important to be where your audience is: YouTube, Twitter, Pinterest, Tumblr and so on.
I have long joked that Facebook is different. On FB, you are “earning the right to pay Facebook to speak to your fans”, and their ongoing changes like hiding the most recent posts and encouraging users only to see the posts that Facebook wants you to see are part of this monetisation strategy.