They're really not that different, especially if you come to DC where everybody in those fields has an M.A. The only way the school makes a difference is its alumni network, which is a huge advantage in finding a job in DC. That being said, you're still going to have to intern somewhere unless you are very, very lucky. An M.A. is certainly not a qualification to work in the policy/think tank/NGO world -- those are extremely competitive jobs and you'll need some internship experience in order to be considered most likely.