Apache vs NginX

Nginx is known for its high performance, stability, rich feature set, simple configuration, and low resource consumption

Nginx is one of a handful of servers written to address the C10K problem. Unlike traditional servers, Nginx doesn't rely on threads to handle requests. Instead it uses a much more scalable event-driven (asynchronous) architecture. This architecture uses small, but more importantly, predictable amounts of memory under load.

Even if you don't expect to handle thousands of simultaneous requests, you can still benefit from Nginx's high-performance and small memory footprint. Nginx scales in all directions: from the smallest VPS all the way up to clusters of servers.

Nginx particularly excels at serving static files—like the Tectonicus map tile images. For larger websites, it's often employed as a front-end Web server to quickly dish up unchanging page content, while passing on requests for dynamic stuff to more complex Apache Web servers running elsewhere. However, I was interested in it purely as a fast single Web server.

http://joeandmotorboat.com/2008/02/28/apache-vs-nginx-web-server-performance-deathmatch/

http://www.wikivs.com/wiki/Apache_vs_nginx

Apache

The drawback to doing everything with processes is that Apache prefork can be a bit of a memory hog, especially under load. Another precompiled flavor of Apache can be installed as an alternative: Apache MPM worker. "Worker" differs from "prefork" in that worker's processes are multithreaded, giving them the ability to service more requests with fewer system resources. This can translate into faster pages served with less RAM and CPU. However, because some Apache modules don't necessarily work well when run under multithreaded Apache, you have to specifically select this version to install on Ubuntu and on other GNU/Linux distros with package management.

Alternatively we can use FastCGI with Apache to handle PHP requests. FastCGI can use a single persistent process which handles many requests over its lifetime

http://www.cyberciti.biz/tips/rhel-centos-fedora-apache2-fastcgi-php-configuration.html

Other Surveys for All Web Servers

http://news.netcraft.com/archives/2011/04/06/april-2011-web-server-survey.html