As someone who's owned both the iPhone 4S and the Galaxy Nexus (and the first iPhone 4, the TBolt, the OG Droid and the Bionic, but hey, who's counting), I'd like to weigh in on this thread.
iPhone display is much crisper/sharper looking than GNex, likely due to higher pixel density and the fact that it has a true RGB stripe. Keep in mind that the pixel densities are not really as close as everyone keeps saying. True pixel density should measure total SUB-pixels. Because the "720p" AMOLED panel in the Nexus uses a pentile matrix, each pixel of resolution only has 2 sub-pixels. The iPhone’s 640x960 LCD panel on the other hand uses a true RGB stripe layout, where each pixel is made up of 3 sub-pixels. The iPhone’s 3.5” display has 1,843,200 (640*960*3) total sub-pixels. The Nexus’ display has the exact same 1,843,200 (720*1280*2) total sub-pixels, but with an extra inch diagonally in which to spread out. The difference is plain to see when you hold the two handsets side by side. That’s not to say that the Samsung’s display is bad –it’s absolutely gorgeous- it’s just not as pixel-rich as the iPhone. In practice, the pentile matrix is all but invisible (much UNLIKE the Droid Bionic which was, to my eyes, barely usable, not to mention completely incapable of rendering some of the primary colors).
iPhone also wins in terms of outdoor readability in daylight. Nexus isn't bad/unusable, but definitely noticeably worse when I'm in the car during the day. It doesn't help that Android's auto-brightness setting renders the display pretty much un-readable in almost any lighting condition, requiring me to constantly adjust the brightness manually. The iPhone is just brighter. While I've heard that other AMOLEDs can sometimes verge on being almost painfully bright, the panel in the GNex seems relatively tame to my eyes.
The Nexus’ AMOLED panel wins hands down in terms of color saturation and contrast. I’m now shocked at the relatively drab, seemingly washed out colors when I pick up my girlfriend’s iPhone. Blacks are deep and colors pop. Sure, the color reproduction may be less accurate… the overblown colors and stark contrast may not suite everyone’s personal taste, but I for one have come to love it. In fact, I find it to be quite well suited to a mobile phone’s typically bright and colorful interface. Though I don’t have any personal experience with it, I can’t help but think that Windows Phone’s metro UI –with its white text on black background and brightly colored tiles- was born to be viewed on AMOLEDs.
I’ve noticed that the Nexus’ AMOLED display seems to add a subtle organic-looking texture (artifact?) to large swaths of solid colors. This is particularly noticeable when viewing large blocks of solid grays, blues, etc, especially with the brightness at lower settings. The calculator app is a great example. Upon first noticing this, I thought it was part of some new graphics rendering that Google had introduced in ICS, but then I noticed that this background texture would remain in place as I scrolled text, etc. over the top of it (again, the calculator is a great example). While I was initially somewhat unnerved by this, I’ve actually come to be quite fond of it --it adds a layer of warmth and depth to the otherwise cold and mechanical user interface.
Though very different in character, the iPhone’s IPS LCD panel and Galaxy Nexus’ 720p AMOLED are two of the most beautiful displays I’ve ever seen in any mobile device –and probably, with the possible exception of the HTC Rezound, THE two best displays available for purchase in any mainstream mobile device at this time. As someone who’s used both extensively, I can assure you that you will be very happy with either display…. iOS, on the other hand, I will make no promises about ;-)
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Travis