C# Best Compatible

Well, C# was built from the ground to use .NET, and only .NET.

Unlike older languages such as VB or C++ it didn't carry any baggage from earlier incarnations which meant that their syntax had to be adapted to use .NET.

However, whether it is still (or ever was) the language which is most compatible with the capabilities of .NET is debatable. It depends what you mean by a 'language'.

The CLR supports a lot more than things than C# or VB support. The current managed version of C++ (known as C++/CLI) supports some of these additional facilities but not all of them. 

The only language which does support all of them is IL itself and it's possible to write .NET applications directly in IL using the ilasm.exe compiler which is part of the .NET framework. In practice few people do - it's a bit like writing a program in assembly language rather than C/C++ though not quite as difficult because IL is higher level than a native code assembler.