The short answer is that zstd is faster and better at compressing than zlib for most input data. For more details, here's a comment I made a couple years ago:

The short answer is that zstd is faster and better at compressing than zlib for most input data. For more details, here's a comment I made a couple years ago: There's a nice comparison of compression algorithms (including zlib, zstd, brotli, snappy, etc) here: https://quixdb.github.io/squash-benchmark/ 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. http://imgur.com/a/0a3kK http://imgur.com/a/0a3kK (the original comment: https://news.ycombinator.com/item?id=12400503 https://news.ycombinator.com/item?id=12400503 )