In my experience, php is better in most cases.
I know a firm [run by one of my best friends] and they develop exclusively in asp.
I had a discussion with him a while ago, shortly after he took on a php / flash developer and started to retrain him in asp.
The guy was forever pointing out how easier it would be to do this / that in php and how many more features [libraries] they could call upon without having to buy in expensive and often buggy COM objects.
At the end of the conversation, he said that had he known about php in more detail _before_ he started out, he wouldn't have chosen asp.
Their overheads are massive, and the enormous burden of the Microsoft Tax doesn't help, either...