I would say smoked MOP. If you want to make it SS only, regular old MOP.
I have a brown horn on my Partenopea SB Sportcoat. That is how it came, and it has more of a worsted look than this. I would much prefer they were smoked MOP....but I am not really interested in changing them.
I do admit that I am not a hater of the gold button...but I don't want to go there.