Honestly, the best part of this episode is to see how necessary it is for Doctors and companions to argue and clash. Rose and Nine have such a lovely relationship and yet they manage to have different moral views affecting their dynamic without breaking it and I love it. It's a beautiful episode as a whole and the cast is amazing, but the one thing in my mind when I think about this episode is always Rose and the Doctor about to die and just how happy they are that at least they're by each other's side. How worth it it was, the moments they had together. Of course they obviously get out of this one as they often will (not... always...) but the foreshadowing goes crazy.