This is my very first attempt with mobile soft and it was my first bet (to use AdMob). But I am going to implement mediation layer to my soft so I would easily be able to "swap" ads and test what brings me best income.
i'm sure that admob doesn't generate a great number, at least not for the iphone. do you have other ad service ?
you can do a/b testing with ads, just put an 'if' in your code and check which service works better for you.