I don't Code ASP so I want you to know that I don't know too* much about the language. However, I have a good friend that is an ASP and PHP Programmer and he says that PHP will always be faster. Now then, on to the facts! ;)
Basically, PHP is used more and it (along with hundreds of thousands of scripts and tutorials) is free. While ASP is yet another way Micro$oft is try to make money.
The only reason ASP is still around is because M$ is backing it (where as PHP only has the Zend Company - and Millions of people -to back it). Kind of like the only reason MSN Search is still around is because it is IE's default search page. (even though google.com is better).
If you want to see some stats look here:
http://www.php.net/usage.php [1]
http://www.tiobe.com/tpci.htm [2]
http://www.dedasys.com/articles/language_popularity.html [3]
Q: What definition of programming languages has been used?A: A language is considered a programming language if it is Turing complete. As a consequence, HTML and XML are not considered programming languages. This also holds for data query language SQL. SQL is not a programming language because it is for instance impossible to write an infinite loop in it. On the other hand, SQL extensions PL/SQL and Transact-SQL are programming languages. ASP and ASP.NET are also not programming languages because these are techniques that makes use of other languages such as JavaScript and VBScript or .NET compatible languages. The same is true for frameworks such as Rails, Cocoa, and AJAX. Finally, we have also excluded assembly languages, although Turing complete, because they have a very different nature.