Reala is finer grained about as contrasty when shot at iso 80, more saturation a wider exposure latitude and better shadow detail than NPS. Reala can handle a 1/500 to 15 minute exposure, NPS might be able to handle a 15 sec exposure. Reala has a fairly neutral palette that leans toward the juicy side that, as exposure or scene contrast increases, goes down right plastic. NPS starts out neutral and ends there.
Npc has about the same grain, more contrast, more saturation, similar lack of shadow detail, and can manage longer exposures better than NPS. I believe that all three films have the extra layer.
NPC and Reala are great general purpose films with both being just okay to good for portraiture. NPS is probably better for in studio portraits.
NPC and Reala are two of my favourite films. I prefer Kodak's 160NC over NPS -- Others would disagree. I find kodak's 400UC similar to or superior to NPC. It is about a stop faster, better in the shadows, as fine grained with maybe a bit more punch.