How to insert / emplace into map to avoid creation of temporary objects?

I'm reading a recommendation from one of C++11 books to prefer emplace over insert when adding items to the container in order to avoid creation of temporary objects (calls of constructors / destructors of the objects being inserted). But I'm a bit confused because there are a few possibilities how one can add an object to the map, e.g.

#include <iostream>
#include <string>
#include <cstdint>
#include <map>

int main()
{
    std::string one     { "one" };
    std::string two     { "two" };

    std::map<uint32_t, std::string> testMap;

    testMap.insert(std::make_pair(1, one));         // 1
    testMap.emplace(2, two);                        // 2
    testMap.insert(std::make_pair(3, "three"));     // 3
    testMap.emplace(4, "four");                     // 4

    using valType = std::map < uint32_t, std::string >::value_type;
    testMap.emplace(valType(5, "five"));            // 5
    testMap.insert(valType(6, "six"));              // 6

    return 0;
}

There are also some under-the-hood-mechanisms involved which are not immediately visible when reading such a code - perfect forwarding, implicit conversions ...

What is the optimal way of adding items to the map container ?