Personally I prefer ASP.NET simply because there's no better development tool than MS Visual Studio and I don't have to pay for it. But I would consider Java (JSP) if I had to - so it would be second best choice. Don't like PHP - an awkward language and a nightmare to debug. No matter what server side technology you choose, sound knowledge of HTML and JavaScript is a must.
Actually a beautiful language to write in and, with even just FirePHP, trivial to debug. But I guess anything is pretty trivial after you've been doing it for many years.
html, PHP, and JAVA all three are used for different purpose. html is simple markup language, php is Scripting language. and java is used for creating the web application and software which is mostly used on the different platform. So for your information just start learning HTML. If you know HTML use then you understand all other automatically..
Another reason to use ASP.NET is that you can program in C#(which is my favourite language) and use technologies line MVC. Together they make it very easy to use JSon, Ajax and make your website SEO-friendly. No need to write HTTP error handlers to redirect request to a virtual path. Maybe these days you can do this just as easily in PHP, but used to be a lot harder in the past.
Well you have to start with HTML for sure. Then choose to study PHP or Java. PHP or Java (if you plan to use Java for creating internet/intranet application) will thereafter be used for generating HTML. Anyway there are three answers to your question: Study, study, study!