Advantages and disadvantages of .php , .asp and .aspx?

There are a lot of differences between ASP and PHP.

1) PHP programs run on Linux, which is free unlike ASP programs one needs IIS installed on a Windows platform server, which is not free.
2) PHP generally uses MySQL, which is freely available. The connectivity of the database is expensive in the case of ASP as MS-SQL is a product of Microsoft that needs to be purchased.
3) PHP code runs faster than ASP [PHP code runs in its own memory space]. ASP is built on COM based architecture, which is an overhead for the server.
4) PHP programs can run on various platforms like Linux, Unix, Windows and Solaris whereas ASP is mainly associated with Windows platforms.[ASP could run on Linux if ASP-APACHE is present]
5) Many of the tools used in PHP are free of cost and since PHP is open source a lot of code can be found in open source forums but in ASP such features are not built in and some additional components are required.
6) PHP is based on C++ language and the syntax used in PHP is quite similar to C/C++. C/C++ is still considered the best programming language by many programmers and people who love this language would surely feel more comfortable with the syntax of PHP. ASP on the other hand has a more Visual Basic kind of syntax that again is closely related to only Microsoft products. So, it depends on a person-to-person which language he or she is comfortable
7) PHP, being extremely flexible, can connect to various databases, the most popular being MySQL. ASP mainly uses MS-SQL.

From my perspective, PHP is an all around better choice than ASP.