What is the difference between HD DVD and Blu-Ray?

OK so I have a 720p T.V and a Blu-Ray player and I know that you need 1080p to get the most out of Blu-Ray. I want to know with even a 720p T.V, will I get more out of Blu-Ray than an HD DVD? If I get Transformers for HD DVD and for Blu-Ray which one will have better graphics? Thanks

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