Best functionnal language?

I have a basic knowledge of how imperative languages work and I'd like to try out a functionnal language. I've heard they are actually slower than imperative languages.
Is that true? If it is, what advantages do those languages bring and what's the most relevant fp language right now?

in C programmer can write same "declaratively recursive with inference" shit but does not
becasue he have cycles conditional and variable which far better all FP shit