thylax,
the definition of diffuse varies from person to person. I am classified as NW5 (may be 4.5). However I have a NW3 hairline (it is oxymoronic to call it a hairline). Diffuse can mean 5% hair loss to 90% hair loss.
If all the hairs I had in the front are moved back, I will be a solid NW4 or 3.5 or if all the hairs are moved to my front and thick, I can grow them longer and hide all my bald spots and look like NW3.
My vote is for a thick NW2, if your hair diffuse hair loss is more than 40% hair loss in density or thickness.
Otherwise I would prefer NW1 with diffuse. The only handicap is that you have to keep the hair dry all the time.