Most green screen is shot for video compositing use today, because high-definition cameras are widely used and are readily available to a broader user base. In addition, green is easier to light with tungsten (artificial) lighting, and it requires less light to illuminate it fully- thus costing less in production for lighting and setup.
For simple chroma keys and mattes, it's the easiest to work with for quick and dirty digital video production. Green is also less likely to conflict with your subject's skin tones, clothing, or eye color than blue. An exception of course is if a subject needs to wear green clothing or you're incorporating natural green foliage into your foreground shot.