I go wherever BDU sends me. After the 24 hours, move to prosperous hunting grounds.
Before the fall of France, I like opening holes on single traffic heading NE for the Fair Isle Passage.
I can't remember the exact BF grid, but locating yourself on a line Between Bristol and the Azores, off the continental shelf is a rich area for convoys.
My standard goal for a convoy attack is 10,000 BRT for four torpedoes.
Coming back to base is as satisfying as a nice greaser landing on an airplane.