The more languages you know, the more marketable you will be. Probably the most in-demand languages are Java and then C++/C#. But just learning languages is not enough to get the best jobs: you also need a solid foundation in programming principles, databases, system design, testing methodologies, etc.
As to whether .NET is "better" than PHP, to some extent that probably depends on what you want to use them for. But probably the biggest edge .NET has is that it has the marketing power of a multi-billion-dollar corporation behind it while PHP is mostly "word of mouth" advertising.