I would suggest, concentrate on both. Content ans link building both are important.
Quality contents are the contents which are unique, has the keywords, understood by the visitors and keep visitors engaged.
If you've posted quality contents then it will definitely increase the traffic on your website or application. From SEO point of view, if there are contents with high rated keywords then it will put your website on top rank. Contents are king because this is the way to impress and invite valued customer towards you.
If there are quality contents then no need of advertising too, you will automatically get the hits.
Now a days, best option for introducing your business is the social media now. Contents which you will placed on it will be followed by thousands of people at a time. It helps to increase the visitors on your website. You can place any type of contents on the social media. You can place audio, video, images anything.
You can use the hash tags in it. Use maximum keywords while posting the contents. You will surely find the difference in the visitors and business.
Link building is is the strategy in the SEO by which you can gain the visitors. There can be back-linking by posting on forum, writing the blogs or by responding to the queries on the forum.
You can also add the internal links that is link from the web-contents from one site to another or from one page to another of the same site.
This become the best option for increasing the visitors.
It depends on the type of links which you are following for the back-linking. Make sure those are not spam links. It takes weeks if you will follow the proper procedure for back-linking.
Here are some more techniques of the link building -
1. Backlining
2. Forum psting
3. Social media posting and commeting
4. Blog posting and commenting
5. Internal links