PageRank has nothing to do with the quality of a link. PageRank has very little effect on ranking.
A quality link is a link from a page with related content. It should ideally be embedded within the content on the page. Ideally, the linking site should ideally already rank well for your targeted keyword phrase. Sidebar and footer links are not quality links. edu and gov links are not quality links unless the content on the page is directly related to the content on the page they point to.
A quality link needs to look like a natural link that someone would use as a reference for the article.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin