For GWX start with this thread.
http://www.subsim.com/radioroom/showthread.php?t=170090
I don't agree with the title of that thread, as there is no 'Best'. Also note that while it says "GWX" in the title, in fact a great many of those mods work with any supermod as well as the stock game. What it really is, is a sampler of what's out there.
As Stiebler said, it always comes down to what you want from your game. I'm kind of caught between the two concepts. There was a time when I just wanted to blow things up. then I graduated to wanting to blow things up realistically. Now I'm at the other extreme: I follow orders exactly and don't complain when I spend an entire patrol and never see an enemy ship. Since I was in the navy and miss it I like seeing all the sights in the harbor and locks in the canals. But that's just me making excuses for myself.
If what you want is to experience hyper-realistic combat I think your choice of NYGM is the right one, and since Stiebler is the man keeping that alive and well his advice is probably the best.
One more thing: Don't ever be afraid to ask more questions about specific details. The people here are dedicated to helping everyone get the most out of the game.
