WAC is beautiful and with lot of action. Best looking submarines ever in SH3.
Not that easy on 100% realism, ships are strong to sink (need more than 1 torp) and with H.sie full patched it’s an interesting experience.
There are additional mods to get snow in winter, and destroyed harbors for late war. Nice touch
NYGM is very interesting too, even though submarines doesn’t match WAC’s ones.
But you can always download and install the German U-Boat Compilation 2 to raise the flag at WAC’s looking!
Stock NYGM submarines are still better than GWX stock ones.
NYGM has the best submarine behavior to me. Not easy to keep an attack at periscope depth without speed...but 1 knot is enough to not slowly sink

100% realism and fully patched with H.sie is a great experience too!
NYGM might be closer to reality as you don’t cross ships every day (as SH5 TWOS BTW)
Harbors are a bit empty, even with the Harbor Traffic add on...not that much to see. But that’s ok, NYGM is more focused on convoys attacks.
Best is to install both, and see what is your preference