I actually only have a few PS2 games left, and no Xbox games. This is why BC isn't an issue for me to consider. The things that I'm considering included the games, online subscription, HD, and overall cost. Oh, and Blu-ray certainly factored in because I'd like to purchase some of this DVD for selected movies (like TDK, for instance).
You're really making this hard then.
Games
Overall the games are a matter of opinion. The overwhelming vast majority of third party games will end up on both consoles. The few that are will likely end up being multiplatform as well.
For the Xbox 360, you have Halo 3, Call of Duty 2, Ninja Gaiden II, Gears of War, Dead or Alive 4, Crackdown and games like Halo Wars, Halo Chronicles, Gears of War 2, Infinite Undiscovery, Splinter Cell: Conviction, and Fable 2 in development.
For the Playstation 3 you have Resistance: Fall of Man, Uncharted: Drake's Fortune, Metal Gear Solid 4: Guns of the Patriots, Warhawk, Ratchet & Clank Future: Tools of Destruction, and games like Final Fantasy Versus XIII, God of War III, Resistance 2, inFamous, LittleBigPlanet, and White Knight Chronicles in development.
And of course there are the multiple games on Xbox Live Arcade (Geometry Wars, Pac-Man: Championship Edition, UNO, Braid, etc.) and Playstation Network (Calling All Cars!, flOw, PixelJunk Eden, etc.) to consider as well.
Of course the die-hard Xbox or Playstation fanboy will tell you that the games on their respective console are the better choice, but it's all a matter of opinion and it's all up to what you personally are interested. Neither console deserves an advantage in this category.
Online Subscription
Right now, Xbox Live and Playstation Network are on par. Xbox Live has Achievement points and Playstation Network has Trophies. Xbox Live has the Xbox Live Marketplace and Playstation Network has the Playstation Store. They both have chat functions, video chat, and instant messaging (Microsoft uses Window Live Messenger in Xbox Live). They both have friend lists. They both have online gameplay.
The only main difference right now is that you have to pay $8.00 a month, $20.00 for three months, or $50.00 a year to have full access to Xbox Live. Playstation Network is completely free. Playstation Network also accepts user generated content while Microsoft does not.
And with the upcomming updates to their services, I gotta give Sony the advantage with this one, Home and Life with Playstation beatout Avatars and Netflix (with Netflix likely ending up on Playstation Network eventually).
However, the Xbox Live Marketplace easily beats the Playstation Store thanks to more content. Both of which are free to access.
HD
Sony takes this one with no debate thanks to the blu-ray capabilties within it. Microsoft offers HD content through the Xbox Live Marketplace, but with the Playstation 3, you don't need an internet connection. Plus they only offer rentals right now.
Cost
This is where Microsoft takes the advantage with Microsoft offering $449.99 for the Xbox 360 Elite, $349.99 for the Xbox 360 Premium (60GB), $299.99 for the Xbox 360 Premium (20GB on clearance), and $279.99 for the Xbox 360 Arcade (which lacks a hard drive). They all offer wireless controllers and a month long trial for Xbox Live. The Elite and Premium models offer headsets and the game Hexic HD. The Arcade model offers an Xbox Live Arcade compilation of popular Xbox Live Arcade games.
Sony offers $399.99 for the 40GB and 80GB Playstation 3s which come with a SIXAXIS controller (40GB) or a DualShock 3 (80GB) and no backwards compatability (meaning that these models suck) and $499.99 for the 80GB Playstation 3 that includes the DualShock 3 controller, backwards compatibility, and Metal Gear Solid 4.