Adding an automatic depth of field effect
Winner: the 7 Plus
This one isn't really a competition, since the 7 Plus is the only camera of the three that provides this feature. "Portrait mode," as it's known, uses both of the 7 Plus's lenses to automatically create an image in which the foreground/subject is crisply in focus and the background is dramatically blurred. As you can see, it looks pretty damn good.
The feature is currently only available to 7 Plus users who've downloaded the beta version of iOS 10.1, but it should roll out to everyone in the near future, along with some additional features that allow for even more control over depth of field.