You can't compare Social Media with SEO. Although, you can say that social media plays a very important role in ranking your webpages higher in SERP's.
Social media only helps to promote your business in social networking websites and generates good traffic from them. They cannot overtake search engine optimization as the later helps to rank your website in search engines.
Social media helps you to promote your website and increase the traffic through social networking sites. But SEO is important for the page ranking and traffic both. So SEO is more important than SMM.