cdn or in-memory cache for stuff you access a lot

Hey everyone, I'm trying to figure out the best way to handle caching for some super high-traffic, read-heavy data that doesn't change much. A CDN helps, sure, but I'm wondering if an in-memory cache, like Redis or Memcached, running closer to our app servers would actually be faster for this. Has anyone here tried both and seen a real difference? What were the trade-offs you thought about, especially when it came to invalidating the cache and network delays?