Centered and above the copyright text is how I did it, because it was the fastest and easiest. It is one possible solution.
But the IDEAL solution would be to have it controlled in the Customizer like this, with the menu and copyright/text in the SAME horizontal row:
This allows the menu to be either by itself, together with copyright/text, or (in the case of the theme I took the snapshot from) with social icons.
This gives the most flexible, and yet user configurable, solution that I have seen.
Hope that helps.