It's been my favorite so far, maybe next to WordFlow. WordFlow's predictave text is quite behind but for accuracy and functionality it's a joy. Outside of Google's recent wonkiness, and just in my own personal view, it's superior to Apple's. I think it depends highly on how one grips the phone when typing, too. I have a friend who can type, with no mistakes, at like 500 words per minute on the default keyboard (seriously, it's super human and obviously 500 is an exagerration of biblical proportions but he's easily over 70 wpm). I grip from the mid so the default keyboard always had a lot of "V's" instead of spaces, not so much with either of the two from MS and Google.
Kind of making me wonder if there are scaling issues that are very subtle with iOS 10. Things have been just slightly off at times. Most likely it's just the new context menus for adding or taking pics and drawing not playing well, right now. Also noticed the Messages app taking the majorit of my battery since installing iOS 10. Anyone else?? Maybe it's the Google keyboard...