Some really good points have been made:
There's always "extern "C"" =P
As C++ is an evolved variant of C, I don't see the point in not using it?
Dont make polls like this. If you were advanced enough to know the reasoning behind the languages, you would also be wise enough to realize a flame war question.
* NOTE: these are just my personal opinions
I found it handy to use a mixture of both. I prefer C and don't care for C++ OOP abilities. I would use Java or .NET if I wanted a pure OOP language. But C++ is very wide spread and still in use today as a common tool. I find what you do with C++ and objects you can acomplish ten times faster with .net and also Java is like a clean OOP version of C, to me anyway. C++ is fast though.
If I had to pick one, I would pick C++ because I can write all the C I want and not have to worry about the ++ part you kill two birds with one stone. I don't think their is any use in arguing which is better, c++ is basically the object version of C.
Now you could argue the OOP features of C++ though, at least compared to other OOP languages.