In this new blog post, Evert Pot talks about getting the most out of your web-based applications through some simple caching types - filesystem, APC, and Memcached.
Caching is very important and really pays off in big internet applications. When you cache the data you're fetching from the database, in a lot of cases the load on your servers can be reduced enormously.
For each of the three caching types, they provide some code and include some discussion around it (like the strategies surrounding using it, problems with its use, and why it would even be used at all). Installations are included where needed (like for the memcached stuff) to get you up and running quickly.
It's not really a comparison so much as just stating what's out there, but it's a good place to start if you're new to caching in your applications.