The fastest language to develop for WP is C++. The core of windows is written in native code (c/c++). If you use a different language, then each time that your code calls framework code, or the other way round (data binding, events), there is a tansition between native and C# / javascript, and back again at the end of the call. This makes apps using C# and javascript slower, compared to C++. Additionally, C# and JS have a "garbage collector" which eats about 10-15% of your performance. In C++ you do the work of the garbage collector yourself, which is more efficient but also more work and more error prone.
So if performance is your main decision point, you should go for C++. However, C++ is rather complicated and difficult to use, if you are not already used to it. I am developing in C# because it allows me to be a lot more productive, compared to C++... For C# vs JS, I think they are more or less on the same level. Maybe C# is a tad faster, but not much. So there it is a matter of taste. If you are already accustomed to one of the languages, it's probably best to stick with it. Personally I prefer C# especially because async programming is easier vompared to JS - and with WP8 and higher you are forced to use async stuff a lot.
10-16-2014 11:38 AM