You can't really put CSS, Javascript, XHTML and PHP all under the class of "web languages". For starters HTML is the markup of the document telling the browser how to display the elements in it. This is the basis for which everything else has been made around. CSS I like to think as an optional extension to HTML that helps splits the markup from the style. Javascript can be used to modify the HTML in real-time aswell as providing the web with the language to program 90% of the pointless "web calculators" out there. PHP just allows you to modify/create the HTML to send to the user on the fly. Of course, all of these things have other purposes, but these are what they are commonly used for.
Going back to what I think you're asking... I use XHTML (strange that isn't it) for what I need HTML to do for me, coupled with a generous dashing of CSS to help the visual impact a little and make it a lot easier to create layouts. I prefer to use PHP over ASP as I know PHP like the back of my hand (how well do I know the back of my hand though?), and I try to avoid Microsoft most of the time (but don't get me wrong, there is nothing wrong with Microsoft, they found a place in the market and expanded on it. Wouldn't you?).
