With Android M, it looks like we're finally getting a way to manage defaults without just using the draconian "reset app preferences" button. Here's what it looks like - just go to apps area in settings and hit the 3-dot menu.
Android Default Apps :
First up, space is being used more efficiently, thanks to the most recent call card no longer being a thing. Previously, in Lollipop, the dialer would display a dismissible card with your last call, showing things like call back, add to contacts, and send SMS. This used a fair bit of screen space, and on Android M, that card thing appears to be gone.