[superMAUS]

First off, C# isn't part of the C family.
You forgot to mention C itself, the mother of pretty much all the other languages.
C, being one step above assembly, is very simple and does not have large amounts of features,
so if you want maximum performance, the smallest executable, C is the way to go.
It is used for kernels, embedded device drivers, device drivers, <good> malware, and some high performance apps.

Every language has it's own advantage, and C being the father and one of the most famous languages ever, in my opinion, should be your next language, I am saying this because you can practice programming without stepping on the complicated things like OOP (I know this from experience).

clap clap clap.

Very true.