Here's some facts which will give you a good idea of how things are at the moment....
1. Porn is pretty much only available on HD-DVD. Blu-Ray has some titles but they are for the most part, only coming from small companies that burn the discs in a PC. HD-DVD replicators number in the dozens with many overseas while Blu-Ray discs are only replicated by Sony (US/ASIA/Europe) and a few other companies here in the US which charge a lot of money for Blu-Ray replication.
2. Blu-Ray has yet to achieve a finalized software standard as they keep adding and changing things in the format which has led to the issue of current players not being able to fully or partially play future titles that are authored under the next version of the format. HD-DVD has it's software figured out for the most part and the only big issues with the format are the combo discs and the new triple-layer disc which supposedly might not work on current players though nobody has actually shown proof that it won't work since there are no discs in production.
3. HD-DVD combos (which unfortunately make up a large amount of new hit films) have serious issues with disc bonding and not playing after you reach a certain point in the movie.
4. Blu-Ray has more bandwidth due to it's capacity which in theory means a better picture and more robust sound since Blu-Ray is able to use uncompressed or lossless audio easily. All the titles released on Blu-Ray (except for a select few from niche companies) that are also released on HD-DVD use the HD-DVD video transfer so there's little if any difference between them apart from audio.
5. HDMI is great as long as you're directly connecting it into the TV but if you connect it to a switch or home theater receiver, you will likely have issues with what is called the "handshake" which automatically configures the video resolution for displays as well as the audio. What that means is that if you have a 1080P TV, a 1080P source such as a Blu-Ray player, and you have 1080P HDMI inputs on your TV, then you should (under normal circumstances) have a perfect 1080P video feed directly into your TV. Now if your TV only had 1080I HDMI inputs (which many cheaper or older displays have) you would not be able to select 1080P output from your Blu-Ray player menus as the TV would not accept it. That also means that if you have a receiver that has an HDMI connection, a TV with HDMI, and an HD source with HDMI, under ideal circumstances (which usually only happens with high end gear or stuff made from one company using the same HDMI chipsets) you can have problems if the equipment says different stuff to each other. For example your HDMI TV might say to the receiver "I can do 1080P", your receiver says the same thing, and your Xbox 360 says it to the receiver as well, but because the HDMI chipsets are different versions with different capabilities, your Xbox 360 won't give you 1080P or your receiver will give you 480p because it couldn't pass the HDMI flow from the 360 to the TV properly. I know that was a long winded bit of info but it's an issue consumers often find out about after they buy a bunch of expensive stuff and it doesn't work as logic suggests it should.
FWIW, I prefer HD-DVD myself