There's a nice comparison of compression algorithms (including zlib, zstd, brotli, snappy, etc) here: https://quixdb.github.io/squash-benchmark/
It's nice because it uses many datasets and machine platforms.
Unfortunately the graphs leave a bit to be desired, especially when you're trying to compare two algorithms. They provide the raw data, but it needs a little munging to make it workable.
For my day job I made the following graph to compare zlib level1 and zstd. This was using the "peltast" platform which is a Xeon based system, because that was most relevant for us.
Imgur album now compares brotli and zstd. Looks like zstd is always significantly faster, but Brotli compresses slightly better for every dataset except the XML one.
This is with brotli level 1, by the way. My understanding is that brotli is pretty quick through the first few levels, but the levels that ask for the highest compression are insanely slow (which is a valuable thing to have as an option, for things like game assets or something, which are compressed once and delivered many times!)
For "compress once, decompress many times" workloads like game assets, you might want to check out Oodle, a proprietary library that kills zstd in decompression speed while achieving better compression ratios.
Unfortunately the graphs leave a bit to be desired, especially when you're trying to compare two algorithms. They provide the raw data, but it needs a little munging to make it workable.
For my day job I made the following graph to compare zlib level1 and zstd. This was using the "peltast" platform which is a Xeon based system, because that was most relevant for us.
http://imgur.com/a/0a3kK
I'll make one with brotli now.