Rose is open, honest, heartfelt, to the point of being selfish, wonderfully selfish. Martha is clever, calm, but rarely says what she’s thinking. Donna is blunt, precise, unfiltered, but with a big heart beneath all that banter. But we come back to what I was saying ages ago about turning characters. If Rose can be selfish, then her finest moments will come when she’s selfless. If Martha keeps quiet, then her moments of revelation - like her goodbye to the Doctor in “Last of the Time Lords”, or stuck with Milo and Cheen in “Gridlock” - make her fly. Donna is magnificently self-centered - not selfish, but she pivots everything around herself, as we all do - so when she opens up and hears the Ood song, or beg for Caecilius’ family to be saved, then she’s wonderful.