I would go white. That way if you change your current color scheme from the white/grey, you won't wish the fireplace didn't have grey. If you are changing this fireplace, you may want to hold off on the area rug you posted about in the other thread.

I love it the way it is. Looks great.

The map on the mantel caught my eye immediately- what a great piece. I agree with the previous poster that your fireplace is fine as it is. It's an elegant look and I think it works well with the walls and floors. Speaking of the walls, do you mind sharing the paint color?.

The paint is sherwin Williams mystikal shade

My vote is for Carrara marble on both!