i want to shoot highly professional green screen video. i am confused between shooting on Canon 5D Mark iii and sony pmw 500 Xdcam hd 422. i want to use 5D but am not sure about its recording format. with H.264 and 4:2:0 will be able to pull of better key? or should i go with sony 500 whhic records 4:2:2 for the best results?
The 4.2.2 color space will always give you a better key. Of course, a 4.2.2 color space will not solve problems with lighting, reflections, etc., but if you set up everything else right, 4.2.2 is better than 4.2.0.
If you're renting a camera you will want to choose one with SDI (or certain cameras with HDMI) and rent either a Nano Flash or KiPro Mini to record to, as this will allow you to go beyond the internal recoding limits of the camera. 4:2:2 at or above 100 Mbps is a good file for green screen.
It sounds like you want to use a single chip camera, I would choose either the Sony FS100/700 or the Sony PMW-F3 and together with and external recorder you will have very professional green screen video files.
If you are purchasing a camera then hands down go with a professional camera like the 500.