Apart from some great release by Universal, Warner have released more content on HD-DVD than Blu Ray. Overall I think the movie selection on HD-DVD is better. People with both players tend to have more HD-DVD discs than Blu-Ray.
Blu Ray on paper has much better major studio support than HD-DVD, although with FOX/MGM going AWOL the difference isn’t that great. HD-DVD has the support of the greater number of studios, because it’s much easier for smaller studios to get content on disc.
Films have different distribution agreements across the world, meaning that a Blu Ray exclusive in the US might be HD-DVD exclusive in Europe or elsewhere. In some cases films there are Blu-Ray exclusive in the US are being released region free on HD-DVD ahead of the Blu-Ray release.
