I had the same quetion when I was at the university. People said 'Don't depend on the technology. Technology keeps changing. Do whatever you like bla bla bla'. But believe me. .NET and PHP is going two different ways.
Once I was an open source believer. But with open source technologies like PHP there is no convention. People keep building add ons and connectors and most of them are not working perfectly. When one thing works then the next one doesn't. You'd have to waste most of your time on struggling with combining open source technologies.
But when it comes to .NET everything is in order. Microsoft handles everything. Their IDE support all their technologies and take care of interconnection between technologies. So what you have to focus is only about your actual project. And you'll get higher salaries compared to PHP developers. But .NET learning curve is bit steep. Once you get pass that you are done!
