This isn't a technical question, but more of a request for advice and empirical/anecdotal data.

I'm nearly done writing a free app for iPhone, and I'm at the stage where I'm going to put ads into the app. I've had mixed success in the past with iAd (their fill rates have been atrocious recently, and their payouts have cut by about 75% over the past 4 months or so), and would like to know how much ad revenue you, the community, has seen from the various ad APIs you've used for your iPhone apps.

This isn't a request for opinion, i.e. which is 'better', only what kinds of numbers you're seeing. I don't need absolute figures, but 'iAd pays x% higher than AdMob, and y% lower than AdSense' would be extremely helpful to me as I make my decision as to which ad API to integrate into my App.

Also, have you had any experience or success with integrating multiple ad APIs into the same app? That's something I'm considering doing in my current iAd-filled apps (particularly my iPad app, which has yet to receive a single impression after nearly 60,000 requests)... something like: 1) Request-from-iAd 2) if that fails, request-from-adSense 3) if that fails, request-from-adMob 4) if that fails, ... etc.