Use `using` in C++ or avoid it?

Question

Discounting subtly different semantics due to ADL, how should I generally use using, and why? Is it situation-dependent (e.g. header which will be #included vs. source file which won't)?

Also, should I prefer ::std:: or std::?

1. Namespace-level using namespace:

   using namespace std;
   
   pair<string::const_iterator, string::const_iterator>
   f(const string &s) {
       return make_pair(s.begin(), s.end());
   }
   

2. Being fully explicit:

   std::pair<std::string::const_iterator, std::string::const_iterator>
   f(const std::string &s) {
       return std::make_pair(s.begin(), s.end());
   }
   

3. Namespace-level using-declarations:

   using std::pair;
   using std::string;
   
   pair<string::const_iterator, string::const_iterator>
   f(const string &s) {
       return make_pair(s.begin(), s.end());
   }
   

4. Function-local using-declarations:

   std::pair<std::string::const_iterator, std::string::const_iterator>
   f(const std::string &s) {
       using std::make_pair;
       return make_pair(s.begin(), s.end());
   }
   

5. Function-local using namespace:

   std::pair<std::string::const_iterator, std::string::const_iterator>
   f(const std::string &s) {
       using namespace std;
       return make_pair(s.begin(), s.end());
   }
   

6. Something else?

_{This is assuming pre-C++14, and thus no return-type-deduction using auto.}