Here's an interesting quote from the American inspectors of the captured German VII U-570:
"In general the submarine has much more equipment to give it stronger offensive characteristics than any submarine of comparable size in either our Navy or the British Navy."
You can see the whole American report here:
http://www.uboatarchive.net/U-570ONIReport.htm
and the British version here:
"Comparison has been made [between the batteries] with standard plate cells of British manufacture. The German cells have a capacity/weight ratio which is about 45 per cent. higher than that of the British cells, but it is estimated that the life of the cells is only 2 to 2-1/2 years."
The British also conclude that her offensive systems are superior to any of theirs. Her torpedo control in particular, but her deck and flack guns as well.
So it looks like the right answer is: the German subs were the best built subs of the war. Pound for pound, nothing else was as generally capable, with the caveat that certain specific missions or goals might be better suited by specialized designs in other Navies.