Few weeks ago i rent one box VPS to test resource usage from three different webservers without any tweaks, it is just basic installation with PHP and MySQL. This three webservers are Apache, Nginx, and LiteSpeed Free Edition. I’m using wordpress basic installation (without any plugins) plus one 404KB image and load it with 50 visitors maximum simultaneously. This VPS has 256MB memory (512MB burst) and using CentOS 5.5 32bit with OpenVZ virtualization. Allright here are the results.
Apache
Nginx
LiteSpeed Free Edition
If you have seen the results of those three tests above, LiteSpeed Free Edition is the least using CPU and memory. Nginx in the second place in memory eating, but probably because Nginx basically do compression of processing static files while on the other side dynamic files serve by FastCGI, it eats more CPU resource. Apache in the third place for memory usage but less CPU eating. Okay so the winner in this test is LiteSpeed Free Edition. You can consider it for your website if you are using low-end VPS, but it only serve maximum 5 virtual hosts, you need to upgrade to paid license for more virtual host. Alternatively you can use Nginx, either ssh based or GUI based via Centmin or Webmin + Nginx modul are available, the only problem is .htaccess compatibility, you need to understand how to convert Apache’s .htaccess. The last choice is Apache for your low-end VPS, but you need to do a couple tweaks and not use too many applications because Apache eats more memory. Anyway there is one more webserver that i have not yet test, it is Lighttpd and will be added soon.