Green screen, this is so if you want to do some film work you have a good patch of screen to use. You can use any colour to key out the background but green is best for this because theoretically human skin has the least green pigment in it that any other colour.
From my experience its always depended on the colors in your foreground subjects ... blue might give better results with all the leather costumes. A little bit of color will get reflected, and blue is a lot easier to hide. The most important thing is evenly lighting it, whichever you choose.