POP_Muzik's comment (#4) is accurate for Phoenix. Unless you take the light rail, you will be competing for parking with the baseball game at the stadium three blocks to the east of US Airways Arena. At 6pm, this eight-block radius is going to get crazy.
I agree with Jason. There's an intamacy to Phoenix's US Airways Center (which is why I chose GA). I think it's interesting that u2.com had floor layouts for the Claw in each venue on the 360 Tour.
... I guess I need to figure out how to upload a jpg into "my media" ...b/c the link (http://360.u2.com/images/largevenues/lg_phoenix.jpg) appears to be broken.