It's not the matter of telling which one is better than the other because they complement each other when it comes to promoting new websites and boosting traffic for them. SMO can be useful because it helps send many visitors to the sites through posting updates and links on hot online hubs, and even if the sites ranks on search engines are not great, a successful SMO strategy will help it.
On the other hand, a great SEO plan will help to ensure the organic rankings of websites improve on Google and other search engines, and since reaching high spots on them can be very effective in sustaining traffic, so no wonder most webmasters and firms focus on their custom SEO programs. It is suggested to use both programs simultaneously to ensure websites traffic shares will be maximum.
You can not choose between them, both have their own qualities. They both can provide you traffic as well as brand value, if you work hard on them. You need to use both of them in a balanced way so you can maximize the result.
SEO(Search Engine Optimization) and SMO(Social Media Optimization) are both the part of SEM(Search Engine Marketing) and both should go hand in hand to get more visitors on the site, however, SEO can be more beneficial in bringing genuine visitors on the site rather than SMO