Not maintained anymore, from what I can tell.
Heliboard is a fork, and quite good: https://github.com/Helium314/HeliBoard
But to *actually* answer your question, I've used #Heliboard, #FUTO Keyboard, and #GBoard interchangeably for a couple weeks now.
The level of frustration and correction on GBoard is just much lower than the other two.
It's proprietary as fudge, but GBoard just has a lot of smarts under the hood.
I have it entirely firewalled off from the internet, of course. ;)