Where C# and .NET really shines is in its native integration and low level facilities. How many other tools in the world let you debug a mixed application containing both native and managed code, all in the same IDE and in the same session, with the ability to set breakpoints in either area, view values, do memory watch points, and so on?
It also feels so incredibly easy to call native code in C#. There's even a whole web site dedicated to making it easier, pinvoke.net!
Lastly, C# itself contains several performance-sensitive features that have no JVM equivalent, including value types, unsigned integrals, and unsafe code with raw pointers. The .NET platform even has an implementation of tail recursion , now, though the C# compile will not generate IL that uses it, which makes it inaccessible for most people.
When it comes to language design, C# is a little sloppy but it more than gets the job done. In terms of tools and low-level facilities for building a real-world application, C# on the Windows .NET platform feels absolutely world-class.
For my favorite language, I of course, voted for Scala!