The difference between Science and Studies is that the Science degree usually requires more coursework in traditional scientific fields, while the Studies degree usually leans toward policy. You do need to carefully study each program, though, to determine requirements, focus, and outcomes.
I'm not an expert in Urban Planning, but a graduate degree in the Environmental world will probably take you in a different direction. I don't know if that is what you are looking for. Without knowing your situation, my guess is that it depends on the angle from which you intend to approach sustainability.