Something popular does not mean it automatically is the best imho.
I chose Python because:
* Easy first language to learn (even easier as not the first one, I guess)
* Very high-level language
* Very advanced Python web-development frameworks (Django, Web2Py, Pylons, etc.)
* Large field of application- for system administration, gui apps, web development, gluing different apps together, lots of open-source apps use Python as a built-in scripting language (for example Gimp, FreeCad, OpenOffice), writing some simple scripts quickly for yourself (for example, to make a backup of important files).
What I don't like about php is it has serious security problems and is not much object-oriented. Perhaps someone else will tell more about its advantages.