After read and see the eCPM in some games, Chartboost and RevMOB gets the best eCPM.
Some info and eCPM stats for RevMOB:
You can find more in this web and other about his eCPM but i thinks looks promising.
I'm looking for an extension developer with experience to create a RevMOB(https://www.revmob.com/) extension for iOS/Android.
This will be for a public release for this reason if somebody want to contribute with some financing are welcomed .
Send me a PM if you are interested with your time/prices