How many servers do you have?
Redis and Memcached are most beneficial/intended for a multiple server setup so if you only have one server, there's probably other/betters thing to worry about. (Best speed increase I've found so far: PHP 7.)
As Brad points out, it all depends on your content, traffic, concurrent users, etc.
It goes without saying having enough ram so you're not swapping can have a huge benefit. Just because those files are stored on disk doesn't mean PHP itself is actually hitting the disk for each request.
SSDs are also now coming standard with a lot of the better hosting plans. SSDs can rival in-memory access times. Just changing your hosting can have a big impact on your app's performance.
If you go down the deamon route, Redis seems more modern and is the newest contender in this space. I haven't extensively used Redis or memached with Craft but I have a client with WP on a dedicated server. We tried memcached awhile back and it was actually slower than without it. It's not hard to see why: there's going to be overhead reading/writing to either daemon—after all they communicate via socket or TCP/IP—and whether that solves your particular performance problem is up for debate.
memcached hasn't really evolved much as of late. While memcached is strictly a key/value store, Redis is intended to store object structures better.
tmpfs could be an alternative as well. It's basically a ram disk and is built into most Linux distros. It's pretty easy to setup and like everything else it has some caveats (making sure it comes back up on reboot, having enough space so you don't swap to begin with, clearing etc).
Some further reading: