I think that each of these approaches can provide good traffic. It all depends on how systematically you act and whether you follow all the rules of the game. According to the data I have read recently, SEO is now considered the most profitable solution according to the statistics. But I know the projects that have become successful thanks to SMM, so I think that any specialist will ensure the growth of your project, if you correctly identify the target audience and understand how to attract the attention of potential customers for a long time.