Well with Germany, I wold go with Subs.
For USA/UK probably a destroyer or battleship.
But really, this all depends on what’s on the board. If there’s a of air power on the other side, then chances are I won’t build subs. If I already have a small navy (say a convoy of transports), I would probably go with a BB. And if I know the other side is using subs, then I probably buy destroyers. It all depends on how you look at it.