Hi Cristina,
I can't speak to Prince2, as I am not familiar with it. However I have much experience with Six Sigma and have found it a valuable process in many parts of my career over the years. It is useful for approaching problems with an analytical and statistical approach; it's very data-driven. I have certifications in both DMAIC and DMEDI. Which one you choose, or whether to pursue both, depends largely on your role and your organization. DMAIC is more for improvement of existing processes and products, whereas DMEDI is geared toward development of new products and processes. Good luck to you with whichever you choose!
Oh, and congrats on passing your PMP exam!