Best Programming Language for Web Development

Web development is something I wish to get familiar with.  There is a high demand for websites by various companies that want to get their names out on the web.  It would also be very easy to show a job interviewer websites I have created in order to show what I can do.  There are a few web projects that I have in mind, but I'm not sure where to start.  First off what programming language should I use?

A couple of my professors have suggested that I use Ruby for web development.  However, it seems PHP is the most popular language for websites as of now with over 81% of websites (source).  Ruby, Python, and JavaScript make up less than 1% of all websites.  Ruby and PHP were both created around the same time, so why is PHP so dominant in web development?  Currently, I do not know much about Ruby or PHP, but I will be learning some Ruby and maybe I can see for myself which language I prefer.

It seems these guys have a preference towards Ruby: