A healthy mix of both will have the maximum impact.
80% of users ignore paid ads in search results as they don’t trust them as much as organic search results (results that aren’t paid for). I’m sure there are plenty of times that you have clicked on a paid ad only to find the landing page experience to be not exactly what you were hoping for. However, the paid ad experience has gotten better over time due to quality scores and creating better online experiences produced by online advertisers. Still, though organically ranking results are 5 times more valuable than paid search ads.
However, those that use a combination of SEO and PPC see an average of 25% more clicks and 27% more profit compared to those who only use a single technique. This is because users see both the ad and the organic search results and that gives them more trust in that particular business.
There are some drawbacks to SEO, though. Once you start on a campaign, it can take 6-9 months of effort before you start seeing results with the best results after 12 months. That is why SEO needs to be a continuous effort. Since it takes longer to build up an SEO reputation, if you do drastic site changes or introduce new products or services, there will be a delay in ranking well for new keywords.