Both are extremely important but Content marketing and writing is more essential than link building because without content, links can't be built. Also you have more freedom with the budget that you're allocating because content writer fees are usually cheaper than link building fees.

where is find good Content writer ?

Thanks for your sharing, I also am doing affiliate marketing

Both content marketing and link-building are important for SEO. But Content Marketing plays a major role in SEO than link-building. Because without content, you can't build back-links.