SEO or SMO are both beneficial. I suggest you do both because they will give good traffic. Well, chances of getting instant traffic usually will come from social media but organic traffic that is continuously is the result of SEO efforts but it usually takes time. If you can do both.
I would suggest SEO any given day, I know for a fact that it can be tedious but you need to understand it's a waiting game. Gone are the days when spamming used to work but now you should no compromise on quality.