For me i will tell you SEO is best SEO brings page rank , visitors, backlinks, alexa ranking ,good keyword position in all search engines etc to your site for life long. and SEO onpage optimization is very important for all websites.
SEO is useful to drive free traffic to websites through off page optimization Process. Social media Optimization is very popular to promote your site and drive more traffic. both are very useful. But SEO is most important.
SEO has a big concept and it has many method for site optimization like SMO,Link Building, Off-Page, On-Page, Black Hat, White Hat and many other. So SMO is a sub part of SEO and SEM. So do not confuse with those concept. Thanks for time.
ya i accept with @stevenyoung point SEO is very important for website in seo there are many activities available. SMO comes under SEO
Coming from a guy with SEO in username this is .. let's say funny I prefer SEO SEM means A lot of money spend constantly ...
I prefer SEO too but can't see the downside of SMO as long as it's kept as a consistent marketing message and with a clear target market defined and well planned it'll be alright. If has to choose between one, I'd say SEO, SMO for me is still not professional enough since it's also a friends, family gathering "place"
Consider what your goals are. Both are good, but focus on the activity that will likely lead to traffic that will convert best.