This question will never go away. 🙂
A bit of correction, like on the SAT. XDCAM EX is not parallel to P2, because, whereas XDCAM is a codec, P2 is a storage medium. P2 can store lots of data in different formats, assigned by your camera. The prosumer HD codec for panasonic is DVCPRO HD. Your question should be comparing XDCAM EX v. DVCPRO HD.
From a data point of view, the issue is the cards can’t store ALL the data so some form of “unacceptable” compression must occur. Panny guys and girls argue that Panasonic is less cruddy than Sony and vice versa. With the Panasonic, there is fancy math that “magically” makes an HD signal. With the Sony, there is fancy math that “erases” the full raster data at persistence of vision, a long GOP.
Other more important factors, IMO, are how does the camera feel in your hand? Does the design match your idea of how a camera should look? (This is important when you pull it out of its case and everyone is looking to see the camera.) What are you going to do with it? What accessories are available that you also need, tripod, lights, matte box, storage, cases, dollies, jibs?
Both cameras are (relatively) inexpensive cameras for a reason.
Where’s my $0.02?