Choose the purpose.
People use search engines and social media for many different parts of their lives. Depending on what your business does will determine which one is the best approach for you. If you’re a local business then I’d recommend going with SEO.
Whenever someone is need of garage door repair services for example. They may be in a huge rush considering they need to get their car out of the garage. For the business that handles that type of customer, I’d highly recommend going after search engines. Whenever someone needs results now they aren’t checking facebook.