I did side by side tests of NPC, NPS, 160NC and 100UC. My impression was that 100UC did have the lowest graininess by a small margin. That's not a measurement, just an observation. What I did measure that surprised me was the speed: 100UC was just the fastest of the three films based on the lower section of the relative exposure/density curves. 160 NC was just the slowest - but they were all in the same ball-park. 100UC also had the longest straight-line section. Caveat: I only tested one film of each type, but they were all developed together and were all fresh.
Whatever, I'd agree with Brian: the choice between them is purely a personal one based on how they look (except maybe for 100UC's apparently greater range - which may or may not matter to you).