Now I must say that I find this discussion highly amusing...
In my opinion it is hardly feasible to compare German U-Boats and US Fleetboats as they were based on completely different design ideas and intended areas of operation.
German U-Boats were strictly planned for merchant warfare, Fleetboats were intended for support of taskforces (it's not their fault, the possible taskforces were bombed into nigh oblivion at the beginning of the war in the Pacific).
As for the technology.... U-Boats were generally smaller than Fleetboats. Even the Type IXD (which happens to be one of the largest operational U-Boats) was smaller than the Balao (also the Type XXI was smaller).
The advantages of the U-Boats over the Fleetboats were generally faster dive times and a deeper dive depths. Also the maneuverability of the U-Boats was greater than that of the US Fleetboats.
Regarding speed, usually the US boats were better because they were designed to keep up with a surface fleet. The U-Boats never had this design notion and being used against slower freighters, speed was less a factor than stealth. One thing has to be noted though.... the speed of the Fleetboats was usually app. 3-4 kn higher on the surface and about 1-2 knots submerged.
As for the range... well... since the Type VII was comparable in size to the S-Class it is hardly surprising that the maximum range was somewhat comparable.
The Type IXC, IXC/41 and IXD had actually a greater range than the Balao.
Regarding the armament... well... the fleetboats had more Torpedos tubes (Balao: 6/4 with 24 Torps in total compare to Type IXC: 4/2 with 22 in total) but then again they where by design thought to act against enemy warships.
One should factor in though that the German torpedos had two advantages.... they were more reliable and had a higher explosive yield than the US counterparts (also the G7e Torp had a way better performance than the Mark 18, which was a copy of the former).
The Type XXI is actually a completely different story not being a dive boat anymore. This thing was designed to completely stay underwater therefore sacrificing surface speed for underwater speed (which was more then 70% higher of that of the Balao). The hull had basic streamlining which no Fleetboat parttaking in operations had in WW2. Actually... fact is that most early post-war submarines of the US shared the hull design of the Type XXI (btw... of the Type XXI 118 were built.... but without bases in France it poses to be somewhat difficult to reach any convoy routes in the Atlantic... especially if the war is lost anyway).
Furthermore... not only the boats were radically different in design concepts... also the type of submarine warfare of both theatres were radically different. The US pitted its submarines against an opponent who had virtually no experience in submarine- and ASW-warfare. The Japanese sonar was not nearly as efficient as the British counterparts, there were virtually no efficient ASW doctrines in the IJN and escort duty was considered a disgrace. Convoys were not common practice and air-coverage was very limited due to the vastness of the area of operations.
Compared to that, the UK adopted the convoy system quite early having experience with that and knowing its efficiency from WW1. The ASW warfare was perfected during the course of the war, providing permanent aircoverage by landbased and escortcarrierbased aircraft, covering the submarine bases as well. Also perfecting detection gear (high frequency direction finder, ASDIC, Radar) and weapons (Hedgehogs) did provide a hard time for the U-Boats.
And finally, the goals of the respective sub-wars were different.... the Germans attempted to choke Great Britain to force peace by cutting supply to their Airforce and Army... the US attempted more to choke vital supplies for the Japanese Airforce and Navy.
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