Me personally I went for the BIA zero skill crews by empty out all my available national blueprints
As for the reason behind my saying are:
1: Your blueprints normal usage are only for researching new tanks which you can just grind out the old fashion way by playing year round.
2: 3D skins and BIA zero skill crews are pretty much the only 2 resource that you can’t really grind by just playing. Even if you willing to pay real money, they are not always available for purchase. And in the event they are available as reward for regular play, they usually required an insane amount of dedicated time to complete in some marathon event