Oh, I have to say Romana; she was much more fun to do but I did enjoy the Princess when she was turning bad.
I think Douglas was a real one-off. He was so clever and so intelligent and so well read in real science that he could make science fiction work as well as it did. And just such fun to have around, he was just such a lovely man.
I like that totally mixed up kind of eclectic group of personal props and bits of costume and I think the fun of doing that is where I was very lucky with Doctor Who.