Ranked in these QuestionsQuestion Ranking
Pro Good support
Staff is available at any Apple store to help explain how to use the OS and debug any issues.
Pro Simple to use
iOS keeps things simple - everything is laid out on the home screens, and there's only one button. The setup process takes a bit longer, but it shows you how to use your device more thoroughly than other operating systems.
iOS on iPad nowadays does everything that the normal user would want.
For Professional use, iOS still falls flat, but even there we're seeing significant advancements. There are more and more fully featured Professional apps. On top of that, Apple is working hard to improve the general workflow with features like Drag and Drop and improved Multitasking.
Con Its not a "Desktop" Operating System
If you use this for: surfing the web, watching videos (ex. YouTube, Netflix) and looking on social sites like Facebook, this is great. If you need something more for work or school, you should go with either a full Mac OSX operating system or Windows. You cannot store certain files or open them locally on your iOS device (ex. store or open .ZIP files), also some programs are not available for iOS that may be available on a MAC OS.
Con iTunes is insane
An iOS device (iPhone/iPad) can be backed up and synced to a Mac or PC, but this is much harder than it should be because iTunes is bloated and complicated.