Its annoying autocorrection tendency to choose 'fir' instead of 'for' frustrates me. People almost never use the word 'fir', but use the word 'for' often. It would be nice if you could blacklist words you want it to never choose.

There is SwiftKey, on the hand, that does those kind of annoying corrections a couple of times, remembers your choice, and does them no more. It's been a long time since I've seen a 'fir' with SwiftKey.