Sorting an array in C?

Which is the best sorting technique to sort the following array and if there are duplicates how to handle them:

int a= {1,3,6,7,1,2};

Also which is the best sorting technique of all?

void BubbleSort(int a[], int array_size)
{
    int i, j, temp;
    for (i = 0; i < (array_size - 1); ++i)
    {
        for (j = 0; j < array_size - 1 - i; ++j )
        {
            if (a[j] > a[j+1])
            {
                temp = a[j+1];
                a[j+1] = a[j];
                a[j] = temp;
            }
        }
    }
}