The best links are natural links from a web site that has a high google page rank value.
What does that mean?
Natural Link = A link someone gives to you because your site is the authority or at least worth looking at in regards to whatever the topic at hand is. The best natural links are text, in the middle of a paragraph, with link text that is a good key-word phrase someone might use to find your site in Google.
If you're looking for the best Gainesville, Florida Real Estate Company, visit the Bosshardt Realty web site. They are localy owned and operated. They have been in business for over 20 years.
This is an ideal natural link. Notice I didn't make the link be "click here" or "www.xyz.com".
As I mentioned above, you want links from web sites with high google "Page Rank" you can tell a site's page reank by downloading the google bar for your web browser. Anything above 4 is good.
So your formula is:
Natural Link + Good Keyword Link Text + Site With Similar Content to Yours + High Page Rank = Very Helpful to Your Search Engine Ranking