It's perhaps unfair to include Jo this high in the list, as she essentially suffers from the same problem Mike Yates did. She simply isn't as good a character as the one immediately before her. Even more unfortunately, she was immediately followed by Sarah Jane Smith, now officially recognised as the favourite companion of everyone in the universe... which doesn't help. Indeed, the immediate effect of Tom Baker refusing to take part in The Five Doctors was Jo getting immediately cut from the episode. She was supposed to appear with Jon Pertwee (she was, after all, his signature companion) but without Tom Baker there to appear with Sarah Jane, there was only one other Doctor for her to logically appear with. And there was simply no way that they were ever going to have the 20th anniversary special without Sarah Jane. So perhaps it's best to view Jo's inclusion at #3 as an indictment of 70's attitudes toward women in general, and Terrance Dicks' specifically. What happened was that in 1970, Doctor Who accidentally solved feminism. They created the character of Liz Shaw, a completely independent, brilliant and self determined scientist who could also rock a miniskirt like there was no tomorrow and had absolutely no compunction about being completely comfortable with being both independent and stunningly beautiful since the whole point was that she was absolutely, 100% in control of her own life and didn't need validation from anyone. Amen to that. This more or less completely invalidated the notion that you had to be either one thing or the other and would probably have solved the whole issue of feminism for the entire western world. Unfortunately, Terrence Dicks made it a point to get rid of the character and replace her with a woman who was a bit stupid and fell down a lot. It's not Katy Manning's fault, of course.