U.S. Armed Forces or New York Police Department?

I'm currently a Sopre at Stony Brook University majoring in Economics. After giving considerable thought in to my life after graduation, I've considered joining the U.S. Armed Forces, preferably the U.S. Navy or U.S. Marine Corps, as an Officer or moving back home to Manhattan and join the New York Police Department. Can someone give me some insight on either of these careers, so I can make my decision?