I have the same issues with the stock keyboard. It replaces words with emails, or even things like "thank you!" Will auto change to "thank I!" For no reason when I'm not spelling anything wrong. SUPER irritating. I'm also a very fast typer so this drives me insane to go back deleting all the time.
I find that Googles keyboards are overall very good but can be a bit laggy and gitchy sometimes. I've had them freeze up before or are laggy to pop up at all.
Swiftkey is also good, especially if you like to change the layout, colors, etc. But I had a hard time getting that one to learn words I needed it to autpcorrect for me.
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