Well, to jump off the SS bandwagon, I will say this:
Stainless steel is heavier, and that can add to avoiding carrying the gun due to weight.
Stainless steel, like nickle or chrome, can be bright enough to be a problem shooting in bright sunshine (i.e. the glare off your gun may cause problems to the shooter).
Brushed stainless steel shows holster wear faster than a good blued gun.
Carbon is harder to remove from stainless steel.
Stainless steel is not rust proof, so care must still be taken to avoid rust.