:| How many times do I have to say this.
I have both, and haha, I bought Gran Turismo like 3 weeks ago, and I've stopped playing it now. Instead, I'm playing Metal Gear Solid 2 on it, emulated because I haven't done so before.
My Xbox 360 is more a part of my life, next to my PC, plugged up to the sound system and monitor.
The PS3 in my opinion is just an extra for playing media, and mostly use it to play DVD's