For me stock autocorrect was always pretty much unusable, but I have no real complaints about the app I use. I'm bilingual and I type in both languages a lot. I remember when I got my first smartphone I bought SwiftKey app (later bought by Microsoft) that made language switching very easy by just swiping the space. Later the app got so good I just left it on default setting and it would still recommend the right words. Since I bought the app it has been always one if first things I installed on a new android phone (I think I had it on an iPhone 3g back in the day too, but I can't remember for sure).

I recently realised how much of a difference it makes when you type quickly as I got an extra work phone with stock android I have to use occasionally.

There is also a feature of this app I use only occasionally, but when I do its great. It let's you type by moving your finger between letters in one continously motion. When one describes it seems rather weird, but it's really one of the best features of the app. You can write really fast this way, the only difficulty it has is with very uncommon words.