PHP is more flexible than .net & it is more flexible for the interaction with the database but .net need some additional managers. Some company use .net & some use php & the salary is purely depends on the company. But there is one major drawback in PHP is that it can be used only for web based development but .net can also be used for application development prefer .net but make sure of your interest. You can succeed with your interest & not with any compulsion.

For more understanding you can download the following files.

ASP VS PHP
Intro to aspnet
PHP Web Dev
Presentation PHP

Thanks