Have you compiled your C code? Is it an executable .exe or a .dll?
If it is a dll, then you can use a Call Library Function Node.
As for you question at which language is better than the other, it depends on how familiar you are with both languages. It is not a matter of quality of language, but rather how fast do you need to implement the solution and how familiar are you with Labview.. And also what the project is...
R