Both are important especially if the keyword has any competition. It is possible to rank a page with very little content with just backlinks though so I would say that high-quality backlinks are more important. But since you are talking about getting a lot of "traffic" then you will need good on-page SEO too.
You need both! Onpage optimization is probably more important because without quality content and the right optimization for Google's spiders it might be tough to get anything ranked.