Stag with a lot of bark looks good on nickel plated guns or blue guns. I'm not really wild about buffalo horn as grip material, though haven't really seen that many.
Though you didn't include it, dark walnut, rosewood, or gaboon ebony all look very nice on nickel plated guns.
And I'm assuming stainless would look pretty close to nickel.
As for me, I prefer wood, stag, ivory, or bone; all natural materials, over plastic anything.