Android has always made it easy to replace default apps, but managing the defaults still isn't very good. Even the recent improvements to the "complete action" dialog box are only half measures. Always or just once? Surely there's room for more nuance? That's what Better Open With gives you.
This app started as an idea on Reddit and has been floating around as a beta, but now it's available to all. You tell this app which apps are your preferred for each action, and then set Better Open With to handle all your defaults. It will automatically open your preferred app for each action after a predetermined number of seconds, but you can also pick a different app from the list. Not sure what to do yet? Hit the pause button. You can also dive into the settings right from the dialog box.
There are a few layout and theme settings, but that's really the gist of Better Open With. More features are planned in the future, but it's a completely free app.