Hey Leo,
You raise a really good question. As you know, one factor that can affect how well a particular load patterns is deformation of the shot that's in it. It is for that reason that magnum lead shot has more antimony than chilled lead shot, to make it harder and less resistant to being deformed at set-back and as it makes its way down the barrel, through the choke and out the muzzle.
Tungsten based shot can vary greatly in hardness, depending upon the other alloys and percentages of each but all that I've seen were much harder than magnum lead shot. It does not deform upon set-back or while on its trip down the bore and out the muzzle. It holds tighter patterns because it cuts through the wind more easily and retains more energy, terminal velocity, than lead shot. Penetration is also enhanced due to all those factors.
Patterning can of course be very dependent upon many other factors, the type of wad used, crimp, powder, muzzle velocity and buffer to name a few.
All things being equal however, harder shot should pattern better than softer shot.
Thanks,
Clark