Global staffing policies

What are the major staffing policies that Global Organizations should consider?

I know there at least three types of staffing policies according to my readings. They are:

1. Ethnocentric: All management positions are filled with employees from the parent company

2. Polycentric: Host country nationals are recruited to manage subsidiaries while management at headquarters is staff by parent-company nationals

3. And Geocentric: Seeks the best people for the job regardless of where they come from

Can you give me an idea on how should an organization chose among these staffing policies? How do you assess the impact of implementing a specific staffing policy?