I had used swiftkey for most of my Android career. I was a huge proprietor of it and even got most of my friends and family to buy over to swiftkey. I had purchased it and even purchased a few themes when they brought out the latest version.
Swiftkey always had the best prediction algorithm and the introduction of "flow" sort of sealed the cake in the box. Then things changed...
How could swiftkey keep up with a tech giant? Google has the research and development centre adequate enough to invent military technology before the military can. Within a few short weeks of the introduction of "flow" by swiftkey, google had released their keyboard to non nexus devices. This was when I decided to give it a try, I mean, it was made by Google and it had a "swipe" feature; so it must be good, right?
That was a couple years back, I had not installed swiftkey on any phone since. Even now, I'm using the Google keyboard to type this. I did try going back to swiftkey for a little bit (that's what my wife uses), but I found it laggy (some letters wouldn't pop up when I typed fast), and the prediction was atrocious. I even tried out a "material" theme. The keyboard was nice, but I just couldn't put my finger on what was not quite right about it... Back to Google I went, and was amazed by how smooth it was.
Game over, swiftkey fought hard, but they just couldn't keep up. Who needs a keyboard with a built in social network, anyway?
TL

R
Used to use swiftkey, tossed up between SK and Google Keyboard, in the end SK just can't keep up.
Differences:
Swiftkey pros:
Can change the shape and side of num pad.
Can very quickly enter ? And !
Themes, customization
Google Keyboard pros:
Can add punctuation very smoothly by "swiping" from the "?123" icon to a punc.
Very smooth and never lags
Minimalistic, Google voice, and amazing swipe (very accurate)
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