diff vs rsync for comparing directories

I am trying to find the most efficient way to compare large directories of media files (RAW photos, 4k video, WAV audio, etc.) on different volumes. I am currently using:

diff -x '.*' -rq --report-identical-files --side-by-side /folder1/ /folde2/

I have a few questions:

1. do diff and rsync --dry-run both use checksum in the same way to verify file contents?
2. is one more efficient than the other in terms of the time required to work through these files and compare them?
3. are there any recommendations for other methods of verifying that the directories and the files in them are the same and looking for any differences still to be copied over?