10 weeks ago
Since those two options are functionally unrelated (at current stage of your career) you are going to need to decide yourself. If you are interested in management/business side of things then go for an MBA. If your interests lie in academic world then getting a PhD is more or less a must.
You always have the option of switching tracks later in your career (once you have some experience under your belt), no matter where you elect to go at this time.