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.