As the Soviets, I would not invest in a large airforce unless you can actually keep up with land equipment demands (infantry, support, artillery, motorized, tank) during full-blown German blitzkrieg in late 1941. In fact, if you can keep up with land equipment, that just means you don't have enough divisions or that your divisions are not big enough. The only planes that should be made are fighters but how many you should make will depend on how the land war is going and how your supply problems look.
As the US, I would definitely invest heavily in all aspects of air production. Naval bombers against Japan, fighters against all enemies, strategic bombers against Germany and Japan. Combine this with the Air Land branch of the Superior Firepower doctrine tree and you get even more bonuses for air.
As the US, I would definitely invest heavily in all aspects of air production. Naval bombers against Japan, fighters against all enemies, strategic bombers against Germany and Japan. Combine this with the Air Land branch of the Superior Firepower doctrine tree and you get even more bonuses for air.