Unless you really, REALLY are looking for an exclusive (Which pretty much narrows it down to either Halo or Fable) you might as well stick with a PS3. All around, it's much more price-effective, lasts longer, and has numerous advantages that the X-Box 360 lacks. See, I might be tempted to say I'm split between the two, until you realize that the cheapest X-Box (Clocking in at around $200) lacks a built in hard drive, any Blu-Ray support, or even wireless internet. Now, paying for internet is one thing, but the inability to connect to the internet is intolerable. Oh, and I guess another deciding factor is that it has over fifty precent failure rates. Even if you were to pay extra, you still lack the wireless internet and Blu-Ray functions. Plus, playing over the internet on the PS3 is free.
So, what I'm really getting at here, is that both systems are inferior to the Virtual Boy. You are foolish for even asking this question. Now go out and enjoy such games as "Water World" or that weird Shin Megami Tensei spin-off.
And to all Kinect fans...
I couldn't type that with a straight face.