9. Clara
Transitioning from companion to companion within the confines of Doctor Who has always been a tricky business. For my money, the greatest strength to look for when greeting a new companion is through the way they change the dynamic with the Doctor. Too similar, and it looks like youre trying to replace the dearly departed. Too different, and you find backlash there too. So far, Clara is walking that fine line, and walking it well. She appears very similar to Amy Pond in several ways (her stubbornness and spunky attitude, especially), but that doesn't mean she is a carbon copy of the fiery redhead. Because Clara is not only new, but a mystery unto herself, we as the audience needed a way to trust her. The scenes between Clara and Merry began to establish that trust if a little girl could believe in her, so could we. Moreover, having her return to help the Doctor at the end of the show deepens our trust of her in her capacity as the Doctors new Companion.