The Windows Phone 8 keyboard fared somewhat better than the stock Android keyboard on this portion of the test, but it was outclassed by both Swype and SwiftKey. And as much as people like to complain about iOS's aggressive autocorrect, it seemed to help reduce the number of errors our testers made as they hammered away on the iPhone's small screen.
Overall iOS looks like the way to go if you want to type rapidly without much fear of sounding like a total twit. The Windows Phone and stock Android keyboards are slower and offer a much less effective form of autocorrect, but chances are you'd quickly learn their quirks if you used them for a lengthy period of time. Similarly, Swype and SwiftKey both benefit from frequent use, as their advanced predictive text capabilities can predict entire sentences based on things you've typed previously.
All testing aside, I recommend that you use the operating system or keyboard you like the most—but never challenge an iPhone owner to a typing race.
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