There isn't a "best" method...what works for others may not work for you.

The real question to answer is: "Where is your audience, and how do they interact with you?"

In my case, FB ads are pointless as my target market is not on Facebook. They are in their corporate offices, being bothered by staff. I have to reach them another way. So no matter how well FB ads may work for someone else, they're not right for me.

Authority blog posts and trade publication articles have worked best for my situation. But again, that may not apply to your business.