If you were to change from your existing mobile OS, what would you swap to? And why?

Let's just assume for a moment that the unthinkable has happened and your current mobile OS has gone under. Which one would you move to as your new choice?

I'm a Windows 10 Mobile user so this isn't entirely theoretical for me... :)

I'm thinking Android. The solid security and curation of Apple's App Store appeals to me but there are too many "choices" that are made for you in iOS. I would value the flexibilty of Android more highly. I'm especially liking the look of the new Pixel devices.