Facebook's ZStandard compression library appears to be both faster and better at compressing than zlib. Is there any reason to continue using zlib for new projects that don't need backward compatibility?
Hm, not really, unless you care about being able to read the data from anywhere else. Zlib, like any of the other "traditional" libraries out there, is supported pretty much everywhere and has bindings for every language you can think of. But that shouldn't drive your project.