Start with your step after you get your PhD and make your way back. If it's for the industry, I would stick with the US. which companies are you targeting? (Google, Microsoft,....) they probably have a preference. Usually it's only companies with R&D that would higher PhDs. If it's academia, it's also important to pick a top tier school. Schools usually hire from the same tier or higher. pay close attention to this on.... Overall if you're looking for employment in the US, stick with the US. Americans we don't know much about the rest of world's universities.