I know someone who got a MPP at JHU and then got a PhD in Public Health there - studying food policy. Here are a few questions to ask yourself:
1. What jobs are you interested in obtaining after graduating? I'd look up your "dream" or "ideal" jobs on indeed, glassdoor, etc. and see what degrees they require-if they tend to require one of the degrees over another, then you have your answer.
2. Are you more interested in a career in international health or health policy and management? (Granted, the two can certainly overlap!)
3. What skills are you hoping to obtain from your degree? Look at the coursework for both degrees and compare - see which one better fits your wants and needs.
Thanks! I'll think carefully about this!