The best kind of backlinks are without a doubt… one way back links from authority sites on indexed pages.
One Way Link
To get the most from a backlink… meaning an increase in search engine rankings, it is best that the link be one way. This means that another site links to you, and you do not link back to that site. Reciprocal links are highly devalued in the search engine algorithms, so much so that I would not even bother with a reciprocal link campaign (unless you are doing three way link exchanges).
Ways to identify whether a site is an authority site is whether it:
1. Has a high Page Rank on the homepage of the site (I would say PR 4 or above)
2. Ranks on the first pages of the search engines for it’s main keywords
While the above is a pretty loose definition of an authority site… it is definitely a definition of a site that is worth getting a link from.
Link on an Indexed Page
For a link to hold any value at all… it must be on a page indexed by the search engines!! Always check to see if the page your link will be on is indexed in Google, Yahoo, and Bing. If the page is not indexed in any of these search engines, the link is useless. On the other hand, if the link page is indexed, the link will have value and help in your search engine rankings.
On a side note… I would also avoid having links on pages that have the word “link” in the url (address). I happen to believe that these pages are devalued by the engines and do not pass any value… or at the very least pass significantly less value.
Happy link building