From the article of WebProNews about Google Shares Percentages for AdSense for Content, Search, this article said that Google has decided to disclose their secret. Google said that the Adsense revenue share are mostly from Adsense for content.
The company says this is an effort to increase about their revenue but for Adsense publisher like us actually have understand of this revenue composition, but may never calculate the composition. Google said the highest revenue are come from Adsense for content, from this service earn a 68% revenue share worldwide. Quote from Mr. Neal Mohan VP, as product management. Other parts are come from the remaining service like Adsense for Search, Adsense for Mobile, Adsense for feed and so on.
Google still continue to make serve for all kind of Adsense service but as business practitioner always calculate the benefit and sharing of each service because each service need cost, if their revenue is too small, Google also will close those service if there are no possibility to improve the performance. Time is always being considered.
About Adsense for search: "We pay our AdSense for search partners a 51% revenue share, worldwide, for the search ads that appear through their implementations," adds Mohan. "As with AdSense for content, the proportion of revenue that we keep reflects our costs, including the significant expense, research and development involved in building and enhancing our core search and AdWords technologies. The AdSense for search revenue share has remained the same since 2005, when we increased it."
John Battelle brought up some confusion around a 15% "serving" fee, known as an "AFC Deduction", which he says was commonly used for negotiated contracts with large publishers, but Google says it was never used for publishers who signed up directly on the Google website. The company told him, "There is no 15% serving, or any other, fee for those online publishers."
So I think the second biggest revenue are come form Adsense for search, but we cannot placed this tool every where because will make bad looking to our site. But we still considered placing this tool in order seen every time our page is viewed.