Ad revenue is, of course, highly dependent on many factors such as app type, traffic, user engagement etc.
I’m largely in agreement with Ingemar.
Experiences will vary, but in my experience Vungle and iAds and AdMob have been the top performers. Chartboost didn’t work well for me (I part company with Ingemar on this one). RevMob used to be great but now, for me at least, has the worst eCPM I have ever experienced. I’m in the process of removing them from my iOS apps. RevMob on Android is a definite no.
YMMV.

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