I have found autocomplete to be just as worthless as autofill.
I dont't even mess with either one at all anymore- in fact I avoid both altogether.
The simple fact is that it is never correct {ok, I will be nice, and say that it is incorrect only 96.99% of the time} and that the time wasted trying to correct the mistakes it causes is easily more than double the time to just type out everything manually.
Not to mention that I no longer spend 20 minutes arguing with my device when I try to spell something unfamiliar to it or to put a period wherever I choose to {and then just giving up and turning the autocomplete off anyway}.