Wordpress Caching- Redis or FastCGI?

each has it's own level of complexity and required understanding you need to deploy and implement and troubleshoot

fastest is = fastcgi_cache but you need to understand both fastcgi_cache and your web application very well including how your site's cookies are configured and which site urls or cookies you want to exclude from caching to prevent logged in members seeing other members data

for centmin mod 123.09beta01 centmin.sh menu option 22 installed redis cache at nginx level also uses memory caching like fastcgi_cache though can be slower but depends on how you configure redis cache. Slower is a relative term as my Wordpress7 demo site is using redis cache at nginx level handling 246-302 million hits/day for 10,000 user Blitz.io test on a 2GB DigitalOcean KVM VPS. Also requires a level of understanding of redis cache (How to install Redis server on Centmin Mod LEMP stack) - wordpress centmin.sh menu option 22 auto install auto installs redis server so that part is taken care of but further tweaking and tuning is left to end user. Again requires an understanding of your web application and cookies so for wordpress means understanding wordpress plugins and their additionally added cookies as to whether you want to custom configure redis to exclude or exclude private data served via wp plugins

the other option by centmin.sh menu option 22 wordpress installer in centmin mod 123.09beta01 is keycdn cache enabler for full page static caching - easier to deploy and requires less understanding of web app and cookies and great for starting out. It's closer to a set and forget configuration. KeyCDN cach enabler is just a better version of Wordpress Super cache for static file caching and it still scales very well some users report 90,000 unique visitors/day on 512MB VPS with Centmin Mod LEMP and wordpress static file caching from WP Super Cache. But isn't as fast as fastcgi_cache or redis cache at nginx level as the cache is served from memory and not disk. But if you know how to do it you can also serve keycdn cache out of a tmpfs ramdisk. But something left to end user to decide and figure out.

FYI, WP Super Cache handled ~237 million hits/day on Blitz.io 8,000 user test on same Wordpress7 demo site server. So looking at Redis cache nginx level blitz.io 10k users at 246-302 million hits/day versus Wordpress Super Cache/Keycdn cache enabler static cache with blitz.io 8k users at 237 million hits/day. Most folks will only ever need KeyCDN Cache enabler for Wordpress