Going by the sentiments at popular Internet forums (including our own comment sections), the outcome of this chapter might be predetermined - Sony's OmniBalance design gets many accolades, while Samsung mostly attracts criticism even after the switch to faux leather (which looks much better than the Galaxy S III / S4 generation).
Here's the rundown. Sony's design involves an aluminum frame that's left exposed on the sides, with two slabs of scratch-resistant glass covering the entirety of the front and back. It may be a fingerprint magnet, but the Xperia Z2 is one of the most attractive devices on the market.
Samsung's design for the Galaxy S5 calls for a Gorilla Glass front, faux perforated leather on the back and a glossy plastic frame along the sides. The back is not everyone's cup of tea, but it hides fingerprints and scratches better and it's got more grip. Plus, it's a notable improvement over the last generation Galaxy S, for what it's worth.
While looks are certainly a key feature of a smartphone (it's always in your hand or on ear), there are more considerations before declaring a winner.
First off, the Galaxy S5 is more compact and lighter. The exact measurements are 142 x 72.5 x 8.1mm and 145g for the Samsung. The Xperia Z2 measures 146.8 x 73.3 x 8.2mm and weighs 163g.
Arguably the most important measurement here is width where both phones are fairly close, but the Sony will still feel bigger if you hold the two one after the other. Do keep in mind the Xperia Z2 has a slightly bigger screen, 5.2", compared to Galaxy S5's 5.1". The displays will be compared in the next chapter.
Both devices are water resistant, but Sony's is IP58 certified while the Galaxy has IP67. In case you're not familiar with IP ratings, the first digit is ingress protection (think dust) and the second is water resistance. A 5 means dust can get in causing only cosmetic damage, while a 6 means no dust can get in at all.
As for the second digit, a 7 indicates the Galaxy S5 can be submerged up to a meter of water for half an hour. With an 8, the Xperia Z2 goes further on both measurements - beyond 1m for over 30 minutes - but the exact maximum isn't specified by the standard (or Sony for that matter).
Keep in mind a meter of water isn't much even in pools. Neither phone will suffer from small dips, but overall there's a smaller chance you'll drown your Xperia Z2 than you will your Galaxy S5 if you go swimming, phone in pocket.
The side keys on both devices are positioned relatively low and are easily reachable. The Sony Xperia Z2 scores some brownie points for its shutter key, even if it's not the most comfortable around. Maybe some will prefer the larger on-screen key but to us, half press is always a perk, phase detect or not.
Speaking of buttons, Samsung is the only major manufacturer that still uses hardware keys (even on its 12.2" tablets!). Those have their advantages, they don't waste screen space for one, and Samsung corrected the main disadvantage - having the Menu key when there's no need for it (since Android 4.0 Ice Cream Sandwich).
The hardware Home key is a necessity on the Galaxy S5 since it houses a fingerprint sensor, the functions of which we'll cover in the software section.
Sony, in turn, has been using on-screen buttons for a while. Some prefer them over hardware keys, others quite the opposite, it comes down to personal choice. The on-screen keys get out of the way in the video player and web browser but still eat up screen real estate elsewhere.
The Samsung Galaxy S5 has a microUSB 3.0 port (more on that later), but both it and the microUSB 2.0 port on the Xperia Z2 are covered by protective flaps for the sake of water resistance. Day to day they prove to be more of a nuisance though as you have to open and close them each time you charge the phone or connect it to a PC.
Sony has a solution to the charging problem - exposed pogo pins can charge the phone even if the USB port flap is closed, but you will need to buy the special dock. Both companies offer wireless charging kits though, although Samsung's implementation is miles better - you just need to replace the back cover. The Sony Xperia Z2 on the other hand needs to be put in a special case for that to work.
Sony's design is daringly angular and involves a completely flat front and back. This means the Xperia Z2 lays flat on a table, completely wobble-free. The loudspeakers doesn't get muffled either, since the phone has stereo front-facing speakers, similar to HTC's One phones.
The Galaxy S5 has only a single loudspeaker on the back with a small nub to keep the speaker from getting completely plugged by the surface it's resting on.
The 16MP camera lens on the Samsung is the second element on the back that protrudes causing wobble. The 20.7MP shooter on the Sony is flush with the back, but just as exposed to scratches.
Below the camera on the Galaxy S5 is another element we'll leave for later, the heart rate monitor.
You can take the back cover off to reveal a 2,800mAh battery, which can easily be swapped out. The battery in the Xperia Z2 is sealed.
Winner: Sony Xperia Z2. It's more attractive - and that's not just us swaying to the popular opinion. It has better water resistance, while the physical shutter key and stereo speakers are definite assets too. The Samsung Galaxy S5 is the more compact of the two and offers a user-accessible battery. The extra sensors try to tip the scales back but fall just short.