The common debate regarding mobile operating system is the Android vs. iOS topic and no yet has ever won from the argument. It is always up to the users which work for them in terms of usage and functionality. The iOS has many amazing features which what makes it one of the top in the mobile technology market, but even something that looks perfect have several flaws hiding behind the curtains.
Straight Forward - iOS is simple to use and requires low need for exploration especially for those users who do not have the time to go through several commands. iPhone has only one physical button and other buttons appear inside the application itself. iOS also hides stuff not needed and has minimal need for the owner to understand about every single thing on the device.
The Alpha - Apple made the first mobile operating system that is very intelligent, representing the icon of smartphones today. iOS is expensive which makes the shift to other platforms less tempting due to the investment by loyal users.
Secure Applications - iOS is one of the mobile operating system with above average security status in dealing with mobile applications. Apple itself filters games and applications from developers before a user sees it at the Apple Store. Another thing that iOS fights for is the piracy war by preventing access to certain download apps that can retrieve music, movies, and games illegally.
Stand-alone - Technically, iOS shares some apps from other sources but the OS has its own operation and withstands being alone. Apple can provide maps, email service, clouding, and virtual assistant exclusively for iOS users only. iOS does not really need to live under the shade of another system.
YouTube has a lot of videos that discuss the strengths by device or model. Here is one on the iOS 6.
Worst Things about iOS
Slow Metamorphosis - iOS isn't exactly like Android which branches out patches and versions every now and then. New versions are created within gaps and commonly under collective results rather than one by one. Another weakness of this is Apple does not immediately address some bugs including the recent lockscreen hack that enables a spectator to bypass the passcode protection provided by iPhone.
Cost - iOS devices are exclusive units and equated as being "royal" devices unlike Android that emulates "democracy" with its open-source feature. Due to this exclusivity of apps, games, and features, iOS devices cost more than most gadgets available in the market.
Also equally numerous on video sharing sites are comments about the weak side of the iOS such as this one.