Frankly speaking nothing is better than the Google network advertisement whether it be for desktop ones or for mobile ones. Keeping this in view, the best ad network suitable for a mobile optimized site is :
AdMob: AdMob is owned by Google and it is basically AdSense for mobile devices. AdMob provides a deep pool of advertisers with the advanced optimization technology and good technical support for developers.
Although AdMob is owned by Google but the AdMob platform works for all major devices which includes Android, iOS, and Windows Phone. This wonderful ad serving platform has an incredible network of more than one million advertisers which ultimately gives developers a significant amount of control in filtering the ads that appear in their apps.
However, AdMob places limitations on ad units that are to be incorporated into apps. All the ads shown are relatively low-impact, traditional banner type:
- 728×90 leaderboard (for iPad / tablet)
- 300×250 rectangle (for iPad / tablet)
- 468×60 banner
- 320×50 mobile leaderboard
AdMob currently allow some specific publishers to run high CPM interstitial ads in mobile apps which pay publishers on a CPM basis but the publisher needs to be selected for this program. Moreover, AdMob allows publishers to set a "refresh rate" on their ad units which will generally result in a higher number of total ads shown and better overall monetization.