It depends on your preference. I worked for a nameplate company for a number of years and generally if it is a brown saddle do brass if it is black do the "silver", unless it has brass fittings or your bridle has brass fittings but most have the "silver" fittings now.
If I were to buy a new saddle (or used with no plate), nothing. But as I just bought a used saddle that had a nameplate, I am replacing it with a silver one (black saddle, silver fittings on everything). I'd rather not have the holes there.
But other than that, I'd say whichever would make you the most happy!