1. Content backlinks (when someone gives a link to your website inside his/her content; for example a blog post or a news article).
2. Site wide backlinks (footer links, blogroll links etc).
3. Website directories (such as dmoz).
4. Blog comments (make sure the blog is do follow).
5. Forum posts or signatures (make sure the forum is do follow).
6. Social bookmaring sites such as Technorati or Digg.

Not all of these backlinks are in the same league though. There are many factors that have an effect on how strong a backlink is:

• Webpage content. If both webpages have a content about the same topic and with similar keywords the backlink will have stronger impact.
• Anchor text (a hyperlink label as it appears on a webpage). Search engines consider anchor text to be very important thus a backlink with an anchor relevant to a keyword will be stronger.
• PageRank. PageRank is an algorithm invented and patended by Google. It counts all hyperlinks and assigns them a weight based on which it is possible to measure a relative importance of an element (a webpage) within a set (World Wide Web). Basically, a link from page A to page B counts as a vote by page A for page B.

So which backlinks are the best?

I have found that content backlinks are by far the most valueable. The problem is these backlinks are very difficult to get as they are created by other people pointing to your website because they find your content interesting and worth linking.

So how to get them? The asnwer is easy: great content. When you fill your website with original useful content people will naturally link to it, they will write blog posts either agreeing or disagreeing with you which will bring up a healthy discussion.

Personally, I don’t find the PageRank to be that important. I would rather get a backlink with a good anchor text from a relevant PR0 website rather than a backlink with poor anchor from PR3 website with irrelevant content. I cannot back this up with any research, this is merely my opinion.

Does that mean other backlinks are worthless?

Absolutely not. They are not as good as content backlinks though.

Blog comments and even forum signatures backlinks have been working pretty good for me. On the other hand, site wide backlinks aren’t worth a special attention. They seem to be performing worse than content backlinks which is logical as they have the same anchor and target URI on all pages (so they probably count just as a single backlink).

Social bookmarking sites backlinks have potential to bring a lot of traffic to your website but they aren’t any better than regular ones.

Conclusion

Do not take this as a word of a professional as SEO is not my main work focus (it’s more of my hobby) and if you find any rubbish in this post – please let me know what you think and write a comment.