I prefer python because I can do more with it. I can do the usual web stuff like cgi, or embed python into webpages like PHP using python server pages or I can use one of the many frameworks like Django or Turbogears to make my site.
Then I can code some shell scripts on my linux boxes and then code some shell extensions or office add-ins on my windows boxes. Hell if I want to throw in a GUI I have plenty of frameworks to chose from
PHP is fantastic for web stuff...python is great for everything
So there...