I have used most of those phones so here imo.
Nexus 4 - Great phone with a crappy camera tbh, in normal day light its nice but once it starts to get a bit dark its crap. The HDR goes someway to fixing this. Software is top notch, battery life is really good since 4.2.2, screen is amazing once you fix it, and I just love the weigth to size ratio, also the very fast.
iPhone 5 - Great screen, really good camera (Behind things like Lumia 920 and HTC One in low light), great build, really good software, very fast.
XZ - Great phone, for the price the SoC is a little dated (Same as the Nexus 4 which is much cheaper device) but it still rather quick. Software isnt to bad, camera is really good, screen is good but with bad viewing angles. The device I find is beautiful but a pain to hold, its very sharp and much large then most other 5" devices.
S3 - Getting a bit old now, but still a solid phone. Good camera, screen, battery life. Removable battery and SD card, and should get 4.2.2 soon.
I currently only a Nexus 4 which I brought from Google for £279 and a 3 Sim only card which cost £15 however came with £79 working out to be an amazing deal. If I had to choice between Nexus 4 and S3 I would go with the Nexus for the software, faster CPU, better screen, the camera is behind thou.