If you have considered shore defences, surface patrols, mines, nets, shallow water, restricted entry arcs, restricted withdrawal arcs, air patrols, weather, day & night raid, actions on [in other words what are your actions going to be if: A,B,C or D occurs] then does it really matter which port.
If you think the tonnage success out weighs the risk then go for it, but remember the crew/U-boat should never be put into a position that you are unable to use the U-boats strengths, depth, decoys, and vertical manoeuvrability are all jeopardised by raiding ports.
I'm not saying you wouldn't be successful, but if a port has limited defences ask yourself "why are there limited defences"?
As you can see I haven't given you a name of a harbour, two reasons, firstly I've never have/will raid a harbour, and secondly I won't be responsible for your U-boat and crew loss if you were KIA, MIA from the harbour name that I gave you.
If you do get a name or two and you do penetrate the harbour and you do sink a large tonnage and you do withdraw and you do make it back to base, then I take my cap off to you and I'll buy you a beer at the Officers Mess.
I remember a true story of Hitler asking a young, keen, war harden captain to do the same thing
.................he and his crew came home to a heroes welcome
My U-boat [U657] achieves the same, but this wolf stays about 30 miles from the route that leads into the harbour [known deep water ambush locations].
Good Luck...........I prey, I can buy that beer for you.