I only ever heard good things about Varnish, Squid, nginx, Caddy and several others.
But IMO the main challenge is having the right caching key; this is why in-app caching is so powerful because you can cache an object through its ID and have any updating logic update the cached object, and any readers will be none the wiser because they’ll fetch it from cache 99% of the time (the other 1% being the object expiring due to TTL policy, or a race condition).
It’s trivially easy to setup many web servers to cache pretty much anything but then it falls on you to always return the right modified / etag response headers. Which is also pretty easy.
All in all, it is a “pick your poison” type of stuff really.
