I am using mobile phones since 1995 and discovered SMS with my friends and even teached Vodafone Support staff about the SMS technology. I owned a variety of smart phones from Motorola to LG, from Samsung to Apple and from Sony to Ericsson.
Samsungs 2560x1440 display is AMOLED as usual and in my opinion by far the best display that Samsung has ever produced. Chances are that your room at night will be brighter than the blacks on the S6.
This means that images have a stunning contrast and a fairly spacious effect. Images, Videos come to live, the jump at you. In short this is the best display I have ever seen on any mobile phone ever. The 577 PPI AMOLED simply pwns the 6 Plus'es 326 PPI SIPS. The iPhone 6 Plus Display is not a bad display by any means but in comparison to the vibrant, contrastful Samsung display, it looses in my opinion - by a clear margin.
The display of the S6 is sharper, has better color reproduction and is much more vibrant
The sound processor of the iPhone transports much more authority (bass) and a tiny bit more clarity, imaging is much better than the Samsung's. Since sound is as important as imagery, the iPhone can take a huge point from this one.
The Samsung S6 feels very premium, the best android phone I ever had in my hand. But damn its slippery – very slippery. The iPhone 6+ is also slippery but not as much and it feels much better in your hand, its an Apple after all, these guys live for premium materials. Yet, the power button is awkwardly placed, the S6 power button is much better placed for your thumb. The huge bezels did not disturb me at all on the iPhone on the contrary I like huge devices, I only wish they made a 6 Plus Plus with 6.5 inch. Long sentence short, better button placement on the S6, much more intelligent Selfie Camera button (on the back), double click camera quick access, etc.. the S6 is so feature laden that its shortcomings in unibody construction and the proneness to error with the soft-touch-keys below the display are made up by superiour technology at the end of the day. It's a tie.
UX, Accessibility, Speed
Lolipop is by far the best advance in Android I have seen. They finally catch up to the UX superiority of an iOS or OSX. It's all there transitions that make sense, that help you to understand where things go and where they come from on your phone. In one sentence: Android 5 is awesome! Yet... this is a device for your palm and you will use it everyday and it has to work flawlessly and there are still flaws in Android's accessibility and touch responsiveness. The iPhone reacts much faster and much more sensible to your touches – yes even if you may say this is a tiny differency – your brain is much faster and it will recognize touch sensitivity as a huge difference even if its small in terms of miliseconds.
Also, again , the soft buttons on the Samsung, I hate them, they are not accessible at all, your eye only sees them when already touched, but guess what Samsung – its too late lightening them up when I touched them, I already touched them after all and don't need to see. WTH Samsung?! Horrible design decision and even makes other Andoird phones a more superiour overall package. Ok, you could root and cyanogenmod your device and lighten those suckers up by default, but this should not be necessary. Let me be clear: You will touch those keys one hundred times a day when you don't want to touch them, they are that bad. Sorry, Samsung, but Apple, once more has the upper hand due to your horrible soft-key implementation. By the way, the finger print reader is on both devices excellent.
Also the screen real estate is bigger, because there is no annoying notification bar when you read your newspapers or browse the Web. Yes, you could hack them away on the Samsung S6, but this should not be necessary. Then again, overall screen usage is a bit better on the S6's Lolipop, great, useful pop ups squeeze everything out of its 5.2“. This is undecidable, since screen size is a matter of personal taste. I like them both.
Battery Life: The battery of the S6 is much better than its reputation. It will last you that 24 hours, rest assured. And with a wireless charger beneath your desk, you can charge them when laying on the table. Yes, thats Uber-Cool and its worth considering an Android with Wireless Charging Capability (Qi-Standart), then again you could easily equip your iPhone with such a charger, but its ugly and not very haptic – Forbes: Wireless QI Charger for iPhone 6+. The battery life of the iPhone is supossedly to be better, but its also a much bigger device, so again this is a unfair comparison and undecidable.
The NFC chip on the iPhone is worthless. Yubikeys won't work. RFID won't work. Wireless SmartCard's won't work. The iPhone is missing the S6's IR blaster as well. Also no Wireless charging. The chargin port on the iPhone is propietery, but by far a better choice than the horrible Micro-USB which I always despised as non-haptic, non-sturdy, error-prone invention. Why and who did invent this, if you know, let me know! Or better don't, I don't care for it, its just bad. If it were for these variables, the S6 would win, but..... this is Apple, there I said it and yes you can buy as many Gadgets, as there are sand on a Barcelona beach. Pro-Grade Sound Equipment like Native Instruments, ProTools, Digital Libraries, Yamaha Drums, Roland, it will all connect first and foremost to the iPhone. There is much more, huindrets of well-made, hand made cases, skins and headphone, camera connectivity kits and so forth. Spigen as a large iPhone case manufacturor who produces innovative quality solution finally creates its entire line (20 case variations at least) for the Sasmung S6 and S6 Edge. Yet the propietery Apple imperium wins this one, especially for perfect integration with the rest of Apple devices, like an iPad or MacOSX. Yes, the iCloud is awesome and the interconnectivity via AirDrop, iMessage and FaceTime a marvel of fine Software Engineering from Apple.
This is a matter of taste. Undecidable, but if you like haptics for the iOS, if you prefer free apps and more variety then go for Android. Apps on iOS tend to have still the edge, e.g. the Wired Co Uk App is much better done on the iPhone. Why? Is this is due to the inability of folks to code with latest Gen HTML5 Fullstack Web Frameworks. Why would anybody sane would want to learn Apple's propietery Objective-C? Are their libraries, their APIs better? I don't know but I will find out. Undecidable topic, it all comes down to what you need.
Last but certainly not least
Win for Android, any day. It's open source. iOS is not, and therefore only God knows how many backdoors the NSA has infiltrated the Apple empire with. Yes these guys actually send Subject Matter Experts as agents to Microsoft, Google and Apple to infiltrate them, it's full-fledged digital war fareagainst human rights these guys are waging and propitery software looses any day. Feel ashamed and hide from my furiousity Apple, for still being propietery in such times. What a shame indeed.
The camera of the S6 is sharper, has better color reproduction, is much more vibrant and is more 3 dimensional, especially when paired with the S6 display and you undoubtely will pair the pictures your camera took with the display of your smartphone.Yes, the Camera of the Samsung S6 wins in my eyes. Well done Samsung!
Of course it all comes down to personal preference. I will keep the iPhone, because its bigger and the sound is better and thus ironically more Android-ish. Android has lost many customers to the new iPhone due to bigger screen size, that's a fact established by well-known pools. Also the iOS UX has still the edge in my eyes, and I listen to a lot of music, being a musician, I really favor a good Digital Audio Converter. In conclusion for me personally the iPhone is the better package.
But... if you favour the best display every known to mankind and the possibly more elegant, sleek design of the S6, featured shortly in the movie Kingsmen, perfectly fitting to the protagonist's tailored suite, and if you dislike the understated design of Apple devices - then by all means go for the Samsung S6 - you will not regret it, guaranteed. It's an awesome smartphone, the best from Android I ever owned, and also street price is €200 Euro less than the price of an iPhone 6 Plus.