Two of my favorite features in Windows Phone 8.1 are the hands-free texting and the Word Flow Keyboard.
With hands-free texting, I can reply to an incoming text without touching or looking at my phone. I can send a new text by pressing two buttons and then not touching or looking at the phone after that. This is great for when I am driving or working on a project like assembling a bookshelf or cooking.
The Word Flow Keyboard allows me to enter long properly spelled words with a few swipes on the keyboard. If two words have similar swipe patterns, Windows Phone will select the one it deems the most likely match but the other possible matches are displayed and can be selected with a single tap.