The best is finding the right balance for your website.
As others mentioned, SEO is compelling because strong search results can have powerful long-term benefits.
But take for example a website that “goes viral” on social networks - this will have a domino effect that could hugely impact your performance in search engines, which is really the best SEO you could ask for.SEO & SMO are deeply related, and hard to separate as one being superior to the other.
PPC is sort of a different beast, but for a big business with the right strategy and budget, can also ignite a powerful effect on social networks, thus leading to improved search placement… you see where I’m going with it.