I thing that It`s hard to define who is the best script language.

HTML is easy to learn. JavaScript can make you web pages more flexible. So If you are beginer you firstly learn the besics of this languages.

The Server Side Langugas ("Server-side refers to operations that are performed by the server in a client-server relationship in computer networking.") give you the power to do you work proffesinaly.

Every Languege is good.
PHP is good for begeners. It`s easy to learn and is one of the most popular server side langiges.

For more powerfull web sites you should use ASP.NET or JSP