pass parameter in std::async or in std::bind?

Here is my class

class Foo
{
    public:
        void foo(const std::string&);
};

int main()
{
    Foo* pFoo = new Foo();
    std::string str = "string";
    //If I want to start an async task, I could do this:
    std::async(std::launch::async, std::bind(&Foo::foo, pFoo,  std::placeholders::_1), str);
    //or do this:
    std::async(std::launch::async, std::bind(&Foo::foo, pFoo, str));
}

So what's the difference?Which way is safer to use?