best practise: Implementation of iAds to iPhone

I'm trying to integrate iAds to iPhone app. It makes me very confusing. my app got many view controllers with uitableviews.

Should I integrate iAds at every view controller or should I add it in mainwindow.xib (i add iAds codes to AppDelegate.h .m) or should I create iAdsViewcontroller.h .m & .xib?

if I add iAds to mianwindow.xib, how do i handle delegates like bannerViewDidLoadAd (need 开发者_高级运维to resize uitableview according to bannerview is visibie or not).

If i integrate at every view controller, banner would be switching along with the app views. I read somewhere if the app doesn't show an Ad for at least 30 seconds, it will lose ecpm.

Any thoughts will be appreciated... =)

Apple iAd Documentation Best Practices