Picture quality. Performance is exactly the same — both have zero shutter lag. All reviews so far show XS is worse than a top of the line Android phone camera from last year.
Shutter performance is less important than time to start.
All tests shows different white balance between pixel and xs. This is highly depends on screens that are used on the phones and photos on iPhone can simply adjusted to iPhone screens.
https://www.theverge.com/2018/9/19/17878018/iphone-xs-x-pixe...
https://www.tomsguide.com/us/iphone-xs-max,review-5747.html
https://youtu.be/tZ9wpMl8pzo