Hi, @Mihai B.! Sometimes, especially for dynamic DB-driven websites, it's obviously good to use Memcached. Keep in mind that Memcached is a back-end caching server. There is also Varnish which is, probably, more popular web caching server and it is a front-end one. Varnish has a lot of configuration options. Then while comparing Memcached which limits key names to 250 bytes and works with plain strings only with Redis which allows key names and values to be as large as 512MB each, I suppose, Redis will be the most universal fitting for speeding-up your websites. Check it out, I hope it will the best solution in your case!
Redis supports more data types than just simple key value as in memcache.
But talking about file system cache, you are talking varnish, which is built specifically for this.
You can also use tmpfs, to store data directly in volatile memory, for performance. But the downfall of having to put data on every reboot.
Personally, I'll amend my former post with this:
Redis and PHP_FPM.
I've not tested others, but having Redis and PHP_FPM setup managed to get my test development to under 1 second from certain places.
YMMV, for me it works a treat. Others will have their own opinion.
LSCache, Redis, Opcache, Memcached, PHP_FPM. Redis is usually around the same popularity as LSCache. Others say Varnish.
Then you get into the whole web server thing, NGINX, Apache, Litespeed.
What kind of website are you talking about caching? Is it a static website? Wordpress? Drupal? Any sort of CMS?