The best doctrine is the Communist path for me, but that differs if you want a good and quick to produce army.
Doctrines come down on how you want to play the game and how you are going to succeed, If you want to be a player that wants a lot of damage dealt to enemies you would choose the Axis doctrine, if you want Development and research and want to expand quicker in technology, then the Allies doctrine is for you. If you choose to be sneaky and want a quick land force that is capable of ambushing, the Japanese doctrine is for you. Prefer quantity over quality then choose the communist doctrine, you can get an entire army on its feet in a minute of hours.
If you want a better example:
