PHP is the best according to my opinion, it's open source like and you can get easily solution of any query.
.Net is also good language for developing an good website but it cost high to get developed website in. While comparing at security to both language then .Net is the best programming language in providing high security.
PHP is very popular, fast, reliable and easy to use programming language. The main advantage of using PHP programming language is that it is absolutely free to use. Therefore, most of the people prefer to use PHP language for web solution.
Both programming languages are best for developing because ASP and PHP websites are more active and can allow users to connect and exchange information using the website's databases.
Both programming languages are best in the field of website but PHP is open source programming language run at various platform but it is not possible on ASP.NET. PHP is very cost effective compare to ASP.NET.
PHP and .NET both are programming language applied to make dynamic Web Pages. Now a day's both are in demand so it's depend on your choice. To choose a language for your project is depends on your project need and requirement.
php - more popular, more job offers, open source
.net - only if you do not yet know enough php to make it fully security, and you know that your service will need high security,
PHP is the best open source programming language because it is very easy to understand and very easy to use. The main advantage of php is it is absuletly free to use. It is more fast as compare to the ASP. Therefore, most of the developers prefer to use PHP language for website development.