What is the most efficient way to set class variable using rvalue in c++?

I just started working with c++11 r-values. I read some tutorials, but I haven't found the answer.

What is the best way (the most efficient way) to set a class variable? Is below code correct or not? (let's assume std::string has defined move constructor and assignment operator).

class StringWrapper
{
private:
    std::string str_;

public:
    StringWrapper() : str_("") {}

    void setString1(std::string&& str) {
      str_ = std::move(str);
    }

    void setString2(const std::string& str) {
      str_ = std::move(str);
    }

    // other possibility?
};

int main() {
    std::string myText("text");

    StringWrapper x1, x2;

    x1.setString?("text"); // I guess here should be setString1
    x2.setString?(myText); // I guess here should be setString2
}

I know that compiler can optimize my code and/or I can use overload functions. I'd like to only know what is the best way.