Having used Draft and Slate, Slate is definitely the choice to go with today if you want something built on top of React.

Draft appears to be essentially somewhat unmaintained, whereas the Slate community has continued to be very active (thanks for the Android support! That's one reason we ended up using Quill for now)

The built-in copy-paste handling is pretty messy to extend compared to Slate, where the system of normalizers works a lot better.