Often players concentrate all of their anti-air defences; don’t do that, unless you are fighting concentrated t3 or t4 gunships without air superiority over your base. Each type of air defence has it’s advantages, you should take advantage of them.
Surface to Air Missiles: Often inappropriately used as the final solution in concentrated air defence. SAM launchers when used in very large well spaced grids with slightly overlapping ranges can saturate huge areas of land or sea making it impossible for enemies to operate aircraft in the area.
Anti-Aircraft Artillery: Flack is the best solution for hardened concentrated air defence.
Mobile Anti-Aircraft Artillery: Completely ignored by the vast majority of players, yet they have become my primary form of land based air defence. T1 and T2 mobile anti-aircraft artillery can always be reorganized to maximize their affect if a region becomes important or irrelevant, you can simply move your air defence. They can also quickly arrange themselves into a well spaced grid when a group is instructed to defend other units or in my case a single wall segment used as an air defence point.
Interceptors: T1 and T3 fights are fantastic for eliminating bombers and other fighters, and as a last resort bringing fire upon gunships.
Gunships: Apparently intended for attacking land based forces, however most players are unaware of their fantastic capacity for destroying other gunships. T2 and T3 gunships are the ideal mobile solution for other T2 and T3 gunships and especially T4 gunships.