Content or link: what is the most efficient for SEO?
You may know the aphorism: "Content is King but Linking is Queen." suggesting that these 2 criteria are of equal importance.
It is possible to rank a page on a keyword that doesn't appear in it thanks to links. It is what is called Google Bombing.
However, as for a "serious" website and a Black Hat SEO method, you will never be able to do it without content. It is both the basis of our SEO and an important part (even essential) of the interest of visitors for your website.
The more competitive your targeted keywords are, the more important popularity will raise.
Consequently, on a keyphrase made up of 5 words that don't appear in any other page, the content will be enough to get ranked. However, on keywords such as "travels", "lending" or "poker", links will mostly make a difference.
The optimization approach you need to focus on will depend both on the main topic of the website and the work already done.
On yet very popular websites, il will sometimes be more cost-effective to invest on new contents. You must deal with this situation on a case-by-case basis.