zopfli produces zlib compatible compressed data, but it compresses much much slower to achieve better compression.
brotli is oriented for text compression. It includes huge built-in dictionary that Google thinks is good for compression. Here it is in readable format: https://gist.github.com/anonymous/f66f6206afe40bea1f06
(raw data is in Appendix A of brotli spec).
I'm pretty sure that zopfli will loose to zstd (in compression ratio and speed). And zstd will beat brotli compression and decompression speed, but will lose in compression ratio for smaller files (because of that built-in dictionary thing). But you can fine tune zstd to also have prebuilt dictionary fine tuned for your data. Then it will beat brotli in compression ratio.