I do not know whether you are better in C# or in Java. But I give you my opinion.
We both know that C# is very modern and really better than Java. You many Microsoft's .Net libraries that can speed up your development and boost your program quality.
But since you want to develop a game, It is really important whether you know XNA or not because further to being familiar with .Net Framework you need to be familiar with XNA and probably a game engine like Farseer.
Final word: If you are a .Net developer I highly recommend you to choose the Mono path because nowadays you can develop many Cross-Platform games and apps using C# which is a very modern language which gives you many possibilites. Further more, if you use MonoGame, since you develop XNA, you can easily port it to Xbox, Windows Phone, iOS, MAC OS X, Windows with just changing a few lines of code.
Answer to your questions:
Which one is less time consuming ? C# and Mono [if you are a .net developer]
Which one has a lower probability facing different devices issues and crashes ? C# and Mono
Regards,
Peyman Mortazavi