namespaces - C++ "using std::" vs calling std:: every time

Let's say I'm using #include in C++ and I'm making a print statement. I can choose either to:

using namespace std;
[...]
cout << "Hello" << endl;

or

using std::cout;
using std::endl;
[...]
cout << "Hello" << endl;

or

std::cout << "Hello" << std::endl;

I'm led to believe, and perhaps this is incorrect, that the first one is somewhat to be avoided, as it can add a lot of unnecessary bloat to your program. However, I don't know if there's any difference between the second and third styles in terms of performance. The majority of code that I see that uses libraries tends to use the third style; however for me if there's no tradeoff in using the second one, it seems like the cleanest and most readable method, especially if you're making a lot of calls to the functions or objects in question.

Can anyone enlighten me?