Using original rules, Germany has no real need for AA guns, especially with the 3 it already starts with. Russia will only have 2 planes for a while, since they will only be able to afford ground troops for the longest time. If it gets to the point where the Allies are attacking Berlin, Rome, or Paris the AA gun is irrelevant. I think the best is to keep one in Germany, one in either Southern or Western Europe (it can move around depending on the situation), and one out somewhere on the Eastern Front.
