i've mainly worked with php, but recently i've done some work on asp pages. below is what i've found in my limited experience with ASP.
PHP Pros
1) A C style syntax, could be a disadvantage if you're not used to it
2) the manual is actually useable and the source code is available
3) functions to handle just about anything. i find myself emulating a lot of php style functions in asp. compare the number of php functions versus the number of asp functions.
PHP Cons
1) if something fails on some setup that you've got to run, you could be SOL. you can submit a bug report but there isn't any guarantee its going to be fixed right away. hmmm, similiar to asp in this regard.
ASP Pros
1) everyone else uses it so it has decent support
2) integrates great with microsoft software. with a commercial add on you can be pulling data from MS SQL databases via ADO and sending massive reports in perfect excel format via exchange email to managers who will never read them.
3) NT authentication can be convenient (mainly used in intranets)
4) easy to setup for complete morons (even i can do it)
5) COM support
6) when is the last time you've heard of someone being fired for using microsoft?
ASP Cons
1) VBScript just looks bad
2) piss poor documentation. many of the books i've found and even the official microsoft VBScript & ASP docs pages are no fun to use.