Which one is essential for SERP's - SEO or SMO ?

Both are good and of equal importance.. SMO for increasing traffic and unique hits and SEO for increasing google Search Engine Rank ing Page.

SEO because SMO is indirectly SEO. SEO is making links and we get links from SMO too. But in recent getting links by doing smo is important coz smo site are more crawlable in comparison to book makring, directory and other sites use to making links.

Both SEO and SMO are important in their own way. But i prefer to SEO.

I believe in SMO like Facebook and twitter ..............

Both SEO and SMO are important in their own way....

I think SEO is more important than SMO..But SMO is also useful in branding of a website or product....

I believe in SMO...and also do SMo for my website.............

I agree with Maitreyee.................

Thanks Maitreyee..........Liked your answer.....

According to my knowledge SEO is more essential than SMO.
SEO has been a common activity of website owners for years now. Although search engine optimization still remains largely a mystery to many webmasters and bloggers, its basic concepts have been, and still are, fairly simple.
SEO – Inbound links are a large determining factor in rankings.
SMO – Links are a result of success, which means that SEO benefits from good SMO.

Both of them are important, but I think SEO is on the 1st place :)

@Grace Hughes - And what about SMO ?

SEO is more important

Leonardo Vazquez -- Thanks for suggestion....

Thanks Anwara......................

Both are good in their own way..SEO is for increasing SERP and SMO to increase traffic and unique hits...

SEO will do just that for you.