I have owned an SD- XD Cam loved it for SD. At the same time owning several DVC Pro Cameras SD. Picture awesome with both. Workflow- incredible with the XD Cam, and also works incredible in high humidity (fog etc…) because it is tapeless. In February I bought 3 DVC Pro HD Cameras. After much research, diliberating, demos, etc…(In fact the real choice is between the Sony HD Cam and Panasonic DVCPro HD) The sony HD Cam may be a little better quality but the Panasonic is so much less.
Back to XDCam Vs. DVCPro HD:
I feel that the DVC Pro HD is much better quality then the 1/2 inch XD Cam. There is really no question about it- if your end product is HD. If you downconvert to SD than the XD Cam might be a decent option. I hear that Sony will come out with a 2/3 version in a year or so.
Hope this helps