The only real advantage I see hddvd having over blu-ray is that you can get combo discs, but I see a number of drawbacks to that. One is that quality control for these combo discs is apparently horrible, DVD-18 is unreliable enough. Another is that it seems to say to me that the hddvd camp doesn't expect its own format to take off. Why else would they bother to include the analog-compatible transfer?
It seems like Blade Runner is going to be WB's acid test for which format is doing better at the moment, because there is absolutely no difference at all between the hddvd and blu-ray releases as far as I know.