Pan's Labyrinth is a very good study case cause there are lots of different encodings out there. Here they are in order of quality:
(1) UK Blu-Ray (VC-1, 28769 kbps)
(2) French HD DVD (VC-1, 20254 kbps)
(3) SkyHD broadcast (h264, ca. 19000 kbps)
(4) German Blu-Ray (h264, 28860 kbps)
(5) USA Blu-Ray & HD DVD (VC-1)
The UK Blu-Ray wins thanks to the higher bitrate. The average bitrate used for the UK Blu-Ray video stream alone is almost as high as the max average bitrate allowed for HD DVD for both audio and video combined. The French HD DVD is quite nice, though, too.