According to Displaymate, the iPhone 5 screen is far superior to just about anything else on the market when it comes to accurately displaying colors and minimizing screen refection. Specifically the company says:
Perhaps the strongest competitor to this new device is the Samsung Galaxy S3 and the company says in comparison, this Korean phone's OLED display has some rough spots - colors are distorted and the screen isn't as bright. Specifically:
Screen Reflectance on the iPhone 5 has decreased substantially – the iPhone 4 has 52 percent brighter reflections than the iPhone 5. This means you won’t be distracted as much by reflections that appear on the screen. The iPhone 5 has among the lowest Reflectance values we have ever measured on a Mobile device.
The iPhone 5 has the highest Contrast Rating for High Ambient Light for any Mobile device we have ever tested, and it’s 57 percent higher than the iPhone 4. This means screen readability in bright ambient lighting has improved substantially – both the image colors and contrast won’t appear as washed out outdoors as on other Smartphones, including the iPhone 4.
The color quality and color accuracy have improved substantially. The iPhone 5 received a Color Gamut and Factory Display Calibration upgrade similar to the new iPad. While it’s not quite as accurate as the Excellent calibration on the new iPad, it is still Very Good and probably more accurate than any consumer display you own (including your HDTV), unless you have a new iPad.
The Brightness is about half of the iPhone 5 due to power limits from the lower power efficiency of OLEDs and concerns regarding premature OLED aging. The Color Gamut is not only much larger than the Standard Color Gamut, which leads to distorted and exaggerated colors, but the Color Gamut is quite lopsided, with Green being a lot more saturated than Red or Blue, which adds a Green color caste to many images. Samsung has not bothered to correct or calibrate their display colors to bring them into closer agreement with the Standard sRGB / Rec.709 Color Gamut, so many images appear over saturated and gaudy. Running Time on battery is less than the iPhone 5 due to the lower power efficiency of OLEDs, even given that the Galaxy S III has a much larger battery capacity and much lower Brightness.The Galaxy S III has a PenTile OLED display, which has only half of the number of Red and Blue sub-pixels as in standard RGB displays, like those on the iPhones. The eye’s resolution for color image detail is lower, so this works well for photographic and video image content, but NOT for computer generated colored text and fine graphics because it produces visible pixelation, moiré, and other very visible artifacts, so a PenTile display is not as sharp as its pixel Resolution and PPI would indicate. PenTile technology does have advantages in manufacturing, aging and cost. For a more detailed analysis see our Samsung Galaxy S OLED Display Technology Shoot-Out.
Moreover the S3 has exaggerated colors - especially green as Samsung did not seem to calibrate their display. It is important to note that Apple has been years ahead in the color calibration game since its desktop publishing days going back to the 1980s. As a person who was responsible for choosing the PC platform for desktop publishing at TMC during those days I can tell you this area was a major PC weakness at the time.
Displaymate has lots of suggestions on how manufacturers can improve their displays and ironically they tell Samsung to focus on making smaller screens so they can be brighter. This tells you part of the reason for Apple's decision not to make a wider phone was to increase its display. Had the phone been wider the battery may not have been able to handle such a bright display on all day.