Alright, it's the styling and finish obviously that makes the first and quite important difference between two gadgets, all the more so when you have two smartphones of similar size, equally slim, powered by nearly the same internals and flaunting a five-inch screen each of HD resolution. So yes, the design does set those two apart.
In this case, apart doesn't even begin to tell the whole story. Both the Xperia Z and the Galaxy S4 are the culmination of decades of engineering experience, design, precision and aesthetics. And while we have no reason to doubt the commitment of either manufacturer to any of those values, it's clear that these Android flagships are based on a different notion of aesthetics.
For Sony, this is a first major breakthrough at the highest level, so an exterior matching the technology inside was a must. And the Xperia Z should be no surprise, coming from a company that has consistently demonstrated its design excellence.
The glass covering the front and back of the handset, the assertively angular styling, the soft rubbery frame that runs around the edges make a perfect ensemble. Undoubtedly, the Xperia Z is very much in the running for the handsomest phone of 2013.
Samsung, on the other hand, is betting on what's proven to work. It would've been way out of its comfort zone if it was to consider anything different than the build and finish that sold by the millions in the shape of Galaxy S III's. We can safely count the earlier two generations as well.
The Galaxy S4 is built entirely out of plastic and looks barely different from the Galaxy s III, except for some subtle details, and has the same Hyperglazed finish (basically, a transparent coating over the plastic). The Samsung flagship looks reasonable - better than the Galaxy S III if you ask us - and raises no doubts whatsoever about long term durability. What it clearly lacks is the premium feel of the Xperia Z.
To top that up, the Xperia Z is IP57-certified for dust and water resistance: it'll survive meter-deep dives for as long as 30 minutes. To make sure no water breaks in, all the phone's ports along the edges are covered with plastic flaps. And that includes a memory card slot too. The price to pay though is a non-removable back cover, and therefore a non-user-replaceable battery, which could be a potential deal breaker for some.
Another negative side to Sony's choice of materials - with all that glass, fingerprints are quite the nuisance. Indeed the Xperia Z turns into a greasy mess in no time, which makes it hard to appreciate the brilliant design. Getting it clean isn't too hard though to be honest, and the white version successfully masks fingerprints.
While certainly not as good-looking, the Galaxy S4 design comes with a number of practical advantages. Not only is it lighter (16 grams), but the removable back cover translates to a user-replaceable battery.
In terms of bulk, both phones are in the same size category. A 5" display of 1080p resolution is the centerpiece and there isn't much space wasted around it. Still the Galaxy S4 is a couple of millimeters shorter and a millimeter narrower, even though it has physical buttons and the Xperia Z sacrifices some screen real estate to accommodate those. Peculiarly, the Galaxy S4 and the Xperia Z are equally slim at 7.9mm.