It's difficult to compare subs of different nationalities, since the respective nations often had different needs in mind due to geography or doctrine. The large US fleet type was originally meant to be scout sub for the battle fleet, but turned out also to be an excellent solitary raider for the vast distances of the Pacific for which it was designed. The German Type VII has horribly cramped but was ideal in the North Atlantic where the distances to patrol areas were shorter and it's slim sonar profile was the margin between life and death in many a depth-charging. The small British 'U' type was ideal for the Mediterranean but not really of use elsewhere due to low endurance. The British had other subs for that purpose tho.
The Japanese subs also were designed for the Pacific. They were large and had excellent endurance, and often scout planes, but weren't deep deep divers and performed sluggishly underwater. Japanese subs suffered primarily from a doctrine that emphasized them as part of the battlefleet and their job was seen as going after other warships. The Japanese never really developed an effective merchant sinking program.
Italian subs. Big conning towers. Poor doctrine. Probably excellent food tho.
