I developed ASP applications for about 3 years and I can honestly say it's awesome for closed environments with limited users. It's very easy to integrate Windows software such as word, excel, etc. into internet applications. The downside is that the security is horrible which is why I say it's great for closed systems, i.e. an intranet. I don't know much about PHP but I would say anything that runs on a Unix platform is a better choice from a security standpoint alone.
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