Android Question AdMob "<Ad Unit Id>": one vs many ?

[b4auser1]

What is more correct and effective to get more incomes ?
Use one "<Ad Unit Id>" for all banners in an application or register a separate "<Ad Unit Id>" for each banner in the application ?
And what about different applications ?

 

[tufanv]

I generally use for id for banners and one id for interstatial. I dont see why you want to use different ad unit for the same type of ad ( for example banner ad) .