@peteorrall
The best I've found for SMS is QUIK:
GitHub - octoshrimpy/quik: The most beautiful SMS messenger for Android - Revived
The most beautiful SMS messenger for Android - Revived - octoshrimpy/quik
GitHub (github.com)
No RCS, but only Google's Messenger has that anyways.
Honestly we should be trying to push past SMS to something better. Matrix or Signal.