I was also a long-time fan of Swiftkey, and switched to OpenBoard a few months ago. The main differences are lack of swipe input which I miss dearly, and slightly less intuitive correction. I think since switching I've put a little more effort into being more accurate which has helped.
FlorisBoard is another open source keyboard project that has experimental support for gesture/swipe typing. It requires a bit more accuracy than spyware keyboards but might be worth a try.
