If you go with Sony you are committed to building a BluRay video library which some consider a next generation Betamax, plus the player is integral to the PS3. The 360 however uses an external HD DVD drive format, if the drive has a problem you need not replace an expensive game console.
There is on the horizon dual capable HD players but honestly I would go with the HD DVD format. And just a bit of side info the porn industry has scorned the Bluray in favor of the HD DVD format, and that is a lot of influence believe it or not.
I agree that the better games like Halo, Gears of War and others are presently made for the 360. Sony has gotten a lame horse with the PS3 unless they can produce a lot of true next generation games.
FWIW... Blu-ray has pulled even with HD DVD and is outpacing it in terms of sales. Also the porn thing turned out to be much ado about nothing as there is porn available in Blu-ray.