Factors that give value to link - known as quality link

In every article corresponding to the link building, you will always read about "quality of link", "build quality links" etc . There you cant find the meaning and explanation of quality of link. The main question here is: How do you determine which of many links in best? How you recognise the quality link?

It is very difficult to define quality links, as what looks good to me may or may not look good to other person. Here i am trying to put the main broad aspect or factors which i might look for considering the quality of links. They are :

• Links from the related website : When i search for links i would prefer the links from the site or web pages which is similar to my website or web page.
• Links From Trusted & authority site : As search engine (google, msn, etc) give more important to the links which comes from the trusted site like .edu and .gov, rather than a link from a normal website.
• Inbound Links (one way) : Search engines give more value on a link that is not reciprocated.
• Links that crawled frequently.
• Links with relevant anchor text.
• Links that can send direct traffic.
• Links from Higher Page Rank.
• Links which is placed in the page which containing content rather than links.
• Link placed in the page where outbound links are less.
• Age of the domain and the age of the links
• Robots.txt excluded page
  

As all the mentioned criteria are not fulfilled while doing link exchange. But it will help you to decide good links from the bulk link. These are the points which i look while doing link exchange.