In my experience the saving over h265 is still consistent and given that hardware h265 is less common that av1 on new devices, from h264 there is no need to go h265 but directly to av1 is better if you need to do the job.

Keep h264 otherwise.

Are you aware that all android devices with A14 have av1 support as a requirement?

Also Apple is adding that, and amazon sticks already support av1 natively.

Said that, indeed h264 is and will be the safest and most supported choice for a very long time.

As 265 goes, not so sure.

I doubt it. In a decade its probably going to be the standard. It just takes time for devices to support it.