Learn them both! One of the best things that could ever happen to me was to be talked down to by an older engineer who said something like “You can’t learn all the programming languages… its very difficult… you are lucky if you can learn one…”. I kind of took that on as a challenge instead of an insult in a time when the internet was just taking off.
Is one better than the other?
No! Why? Because they are two seperate and distinct things like apples and oranges or Honda and Ferrari. Lets take the Honda/Ferrari example for a spin. I have seen many people pump tons of cash to create a high performance Honda for racing. Custom Suspension, Turbos, Tires you name it. But it will never perform and compare to a Ferrari. Both are cars and will get you from one point to the next and thats pretty much where the similarities end. Now one will cost next to nothing and be efficient while the other will cost you much more and be a bit of a burden to maintain.
At this point in the internet game you need to know PHP. Its free, widely adopted, hosting is less expensive and many great applications like this wordpress blog are available at no cost. PHP is optimized for the web and is a straight forward scripting language that is easy to pick up and if you run into trouble guess what? Tons of info and help is available online at no cost to you.
Theoretically you could build just about anything you need for the web with PHP like websites, webservices,
scrapers data aggregation, wordpress plugins, etc… I have “seen” PHP scripts that can do anything from login to websites, create email accounts, blog spam auto update blogs to generating images and flash files. With some work you can even simulate multi threading but in the end its not true multi threading and thats where .Net starts to shine
If you need data crunching reporting or massive multi threaded applications .Net whether its c#, c++ or Visual Basic is going to be the way you want to go. And guess what? Microsoft offers its .Net Visual Studio development software for free!
.Net can create powerful windows tools but unfortunately at the moment in my opinion gets out done by PHP when it comes to the web. PHP was developed for the web around proven and efficient platforms while .Net still has a windows application mindset towards web development.
As a coder you are only as good as what you can create. If you limit yourself to PHP or .Net you limit your ability to create and more importantly your opportunities of which there are many.