Initial comparative camera shots taken from almost all of the flagships phones on the market right now, including the Sony Xperia Z1, Nokia Lumia 1020, Nexus 4/5, and iPhone 5s, are out.
Looking at the pictures, seems like the Lumia is the clear winner. Nexus 5 camera is probably second. iPhone camera doesn't seem like it can keep up and I'm surprised how bad the Nexus 4 camera was. Zoom in on the detail on the sign and on the Lumia and N5 you can still tell the specific orientation of the screws holding the sign up, the detail is lost on all other phones.
Lumia 1020
iPhone 5s
Nexus 5
Samsung GS4
Source