Which one should you buy?  Here si the simple answer: Get a blu-ray.  Why do you ask?  Because blu-ray has the most support, it is beating out in sales the HD DVD 2:1, it has true 1080P output, and its a great piece of hardware when it comes with a PS3.  I love my PS3 and I use it to play videos and movies all the time.  In fact, I have a network drive which is on a server which has bunch of movies that it pulls from.  It will eventually play Divx videos soon.