I tried Gboard and Wordflow, both are good swiping keyboards - much better than Swiftkey and Swype but still prefer Apple's stock keyboard, it has improved at predicting words .. even contextual words in a sentence - that makes swiping keyboards feel more cumbersome where you still have to correct a few words every time. Apple hasn't probably hasn't mentioned this but it's word prediction has improved considerably.
I also think QWERTY is not the ideal layout for a swiping keyboard - feels weird constantly rubbing on the screen from one end to the other, hoping that the right word pops up on t he screen and do the rubbing all over again.
Only thing I wish is on the Apple's stock keyboard there could be more than 3 predicted words.