Yeah, the tweaks Fifi's NYGM has in many aspects of the simulation are outstanding and it feels both very realistic and right on the point for me. The environment and the graphics are also great. I really enjoy playing this mod.
In the other hand what I like of GWX KC is the fast loading times, the unified campaign, the GUI (outstanding) and the night lightning inside of the sub at night (no red lights).
I play both of them