When to use PHP or ASP.NET? [closed]

Question

I have worked extensively in developing web applications using PHP and ASP.NET, but one of the questions that I'm constantly asked by customers is whether to move forward with a php website or an asp.net website.

So naturally the first thing that comes to mind is to answer the question like this:

PHP is open-source and ASP.NET is from Microsoft.

Usually after something like that is said the customer has a blank look on there face. Apparently the fact that one is open source and the other isn't doesn't really faze them. And for good reason, because when I first heard it, it really doesn't tell me much.

I know from working with both that each have their differences when it comes to developing websites.

My question is what are differences between ASP.NET and PHP as far as

1. Features
2. Security
3. Extendability
4. Frameworks
5. Average Development Time

I am trying to compile a list of facts to be able to compare with the customer so that an informed choice on the appropriate development platform can be made.