Use the map thats all I got to say on that.
NE of Ireland, convoy route and lots of lone merchants, but high air coverage and warships pass often.
West of Gibraltar, massive convoy route, lots of lone merchants, lots air cover and tonnes of warships but mush bigger game as well.
Thats where I go mostly although it never hurts to explore and I know that the BE area is full of ships, convoys and planes.
As far as I know you're pretty new to this so I think it would be better to leave the first two till you get to grips with the game and all, but its your choice.
