I think most languages are the same. There is a productivity vs. speed tradeoff, but:
A functional programming style, can be done in C if you just accept that minimizing global variables and pass functions by their pointers. Learning a functional language is likely to improve your C style and pointer management faster than how you might develop a functional style out of your own assumptions of what it might mean.
Class based OOP programming can also be done with C implementations. The only benefit of OOP is that it lets you write more without thinking first. Defining data types first and data organization, and then later simply patching them together. Its very similar to relational DB models. Most programming is done this way, because it is the most accessible to people to write code before understanding the problem. Its very useful when the problem comes from someone else and not perfectly specified.
One exceptionally highly productive language that still fits both of the above paradigms but also expands your solution processes is J (Jsoftware.com).
Regardless of how popular it is, this language can be the best tool for some to most applications. If you were paying for your own time, you might use it if you know it. But even if you only care about employability, J will make your programming in any language better, because a consise J solution tends to map to a consise solution in other languages.