Who is a preferred sponsoring the PMO?

In my view as a certified project director (CPD), I would recommend the PMO to have a "director level executive"  that reports to the board of directors or a a designated high-level function as the "corporate development unit"  (CDU) if such a thing exists in the organization.  Eexecutive-level sponsors are needed at the project and program level to ensure each and every project/program gets its fair chance for execution and success !!