Which traffic is the best for Adsense

The traffic from what search engines  is better converted on Adsense? For the sake of interest has made sample on 10 MFA websites for last month.
And marvellously the result is identical to all 10 websites.
This is my percent of clicks on 1000 visitors on 10  MFA websites:

• search 20,55 %
• yahoo 16,36 %
• msn 16.3 %
• ask 15,15 %
• aol 13,99 %
• google 10,90 %
• netscape 5,56 %

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