Apache MPMs - Worker vs Prefork

You should use prefork when using apache + mod_php. The FAQ clearly outlines the reason why:

http://www.php.net/manual/en/faq.installation.php#faq.installation.apache2

Why shouldn't I use Apache2 with a threaded MPM in a production environment?

PHP is glue. It is the glue used to build cool web applications by sticking dozens of 3rd-party libraries together and making it all appear as one coherent entity through an intuitive and easy to learn language interface. The flexibility and power of PHP relies on the stability and robustness of the underlying platform. It needs a working OS, a working web server and working 3rd-party libraries to glue together. When any of these stop working PHP needs ways to identify the problems and fix them quickly. When you make the underlying framework more complex by not having completely separate execution threads, completely separate memory segments and a strong sandbox for each request to play in, further weaknesses are introduced into PHP's system.

nginx + php-fpm is also an excellent way to run php applications. nginx has native support for FastCGI and php-fpm is one of the best ways to run php in a FastCGI environment. See the php documentation here:

http://www.php.net/manual/en/install.fpm.php