Funny you ask, I integrated AdMob into our mobile site last night... it was painless. We're also integrating it into our physical iphone app but that's still a WIP. I don't have any statistics for you, we just started with AdMob.

I really like that they offer progressive loading with their .js system so your app content loads first, then the ad will load. This is pretty important to me so that Edge users don't suffer, and a quality customer experience is prioritized above ads. I believe they track this metric as "fill rate" if I'm not mistaken.

On 'story' pages, I can actually fit 3 ads pretty nicely but I credit this more to the applications design which is heavy in text-content.

http://m.breakkup.com

I selected AdMob because their system seems to be the most robust for our needs... I also like the empowerment campaign they are doing giving away $1m to developers. I hope some of it trickles down to the bootstrappers. :)

Feel free to reach out, be happy to keep you posted about our results and experience.