Here’s a very useful criteria for how Google values links. If you click on the original article you can go to the last page to get to the conclusion. Basically the author is saying that right now Google prefers websites with high quality links where Bing prefers sites with a high volume of anchor links. Of course this could be outdated by tomorrow, but for now I think this link quality criteria is pretty helpful.

For the purpose of analyzing the quality of links, considering the criteria explained above, the following rating system is formulated for link location:

1 point – link appears in footer or other portion of the web page (not in the body).

2 points link appears in a blog roll or special resource section of the website and not in the content.

4 points – links appear in the content /article

Domain relevance rating system:

1 point – no relevance at all to the targeted website.

2 point – medium relevance, not direct (for example, if back links are from SEO websites pointing to PHP websites), or not directly related but somehow connected to each other.

4 points – links coming from a directly relevant website. (PHP to PHP-based websites)