Hello Stefan,
Thank you for reaching out and I am happy to assist you with this.
Gzip was designed specifically to compress files. The library has been incorporated into a lot of different programs that need to compress files. The library was incorporated into web servers as compressing content started to be the norm. It was one of two compression algorithms specified in RFC 2616, the HTTPS 1.1 specification. While it wasn’t specifically designed for streaming operations like web servers, it was adapted to it.
Brotli, on the other hand, was specifically designed for the web. Google recognized the need for a way to compress streams more efficiently so they designed Brotli.
If you have both settings enabled in the W3 Total Cache Browser Cache section, most of the modern browsers will favor Brotli compression and the ones that do not support it (very few) will show Gzip.
I hope this answers your question.
Thanks!