From what I’ve seen on the market, Nginx and Cherokee are pretty interchangeable for what you’re doing. If you’ve already got things set up on Nginx … there’s no reason to switch to a different system.
But if you want some benchmarks … I did a quick Google search and came up with these:
- http://blog.mudy.info/2009/02/nginx-vs-cherokee/
- http://arnisoft.com/239/server-benchmark-apache-nginx-cherokee/
In the end, it all depends on what you care about the most. If you’re running WordPress with caching enabled, you’ll be more concerned with static content. If you’re running a multisite installation without caching (something I do), you’ll likely be more concerned with dynamic content and stability/security.
From a general usability standpoint, though, it’s safe to look at the market leaders and use them as a canary-in-a-coal-mine.
WordPress.org recommends Apache for a server because it’s easy to set up and comes pre-configured on most hosts. However, Automattic elected to use Nginx to host WordPress.com. They have their own reasons … but I elected to do the same for performance reasons (and so I can run some asynchronous servers using the same system via Node.JS).