I havént hit any ports in a few patrols, so I can't remember much but here goes..
Port: Reason
Scapa Flow: Home base of the RN, plus good targets.
Bristol: Good targets
Liverpool: Few but ok targets
New York: The best port I've ever hit, 125k tonnage in there, and plenty of renown.
Loch Ewe: Respawning Nelson, easy tonnage, when suffering from patrol blues.
Hartlepool, SouthEnd: Can't remember but was worth it.
Halifax: Have'nt tried this one yet but I expect it to be rich.
Trinidad/Tobago/Curacao: Easy tankers.
Galverston: Tanker Heaven
Miami: can't remember but was worth it.
Key West: There is a liner here IIRC.
Norfolk: A couple of troop transposrts and tankers, but EXTREMELY dangerous. I'd say the worst port to get into.