GS4 is the way to go.
-Best camera in Android
-Incredible Display
-Very compact and lite build for a 5inch screen phone, it feels like it falls between the GS2 and GS3.
-Here in SA the GS4's are mostly 32GB variants
-Huge 2600mAh battery, great batt life
-Great performance especially with the latest ROMs
-Great after sales service by Samsung with ADH
-CPU/GPU 2nd ONLY to the Snapdragon S800, currently we don't have any phones here based on the S800.
-Tons of other awesome features.
Played with a Xperia Z on Sunday, wasn't that impressed, display was very dull compared to my GS4's even at the same brightness, Z seemed washed out, also the Z isn't as hand friendly as the GS4, its wider and with sharp edges, just not as great in-hand as the GS4.
Have to agree!!
Used both the Z and the One but S4 is still the best, and yes Z was on latest update.
They all very nice phones but all things considered S4 takes it.