Format: Sony XDCam HD
Use: XDCam EX 1080p24
As far as the VBR vs CBR thing...I actually didn't know XDCam did both. Is there an setting that you are able to choose in the camera when you're shooting? I'd go with whatever your camera recorded. If you don't know what your camera recorded, I would ASSUME VBR is better because I know ProRes is a VBR codec. But that's just an assumption, I'm not positive.
For ProRes, all you need is ProRes422, HQ is overkill.