Sayaka and Kyoko are kind of like hero falling and anti-hero, Sayaka is all positive and aiming for the good side, but it starts to fall apart and at the end and becomes a witch. Kyoko seems all hardcore and dark at first but ends up slowly moving the other way and ultimately being the one to sacrifice herself to save Sayaka and everyone.
Meanwhile, Madoka and Homura are like polar opposites, Madoka has the good heart and hates to get involved until the very end, when she finally lets go and does the one thing she can do for Homura. Homura was all stiff, keeping it all in the entire time, sacrifice after sacrifice, but then she finally lets go at the very end and acccepts Madoka's gift.
Mami I think was just saying that the archetypical super-person that conquers everything and is victorious all the time isn't going to win this time, it seemed to be saying, this is going to be a story about the other people who are constantly driving after their other halves, not the one super person.