2. Shona McCullough
Shona is the most recent potential companion and easily one of the most popular judging by the sheer amount of calls for her return. She was part of the shared dream state induced by the Dream Crabs (don't think about them... too late, one is coming for you...) in Last Christmas. The others tended to put her down and didn't really take her seriously, but she was the stand out from the opening moments, especially with that dance scene. Deceptively observant and inquisitive but with the potential to walk into trouble, it's easy to see how Shona could be a good companion. There's also a lot more to her character that's yet to be revealed (who's Dave and why does he need forgiving?), giving fans more reason to want her back. Of course, never having met the Doctor in the flesh is a huge problem - their interactions were only part of a huge trippy dream. Going by what the Doctor says, it's questionable that any of them will even remember their dream, so meeting in the real world may be even more difficult as they might not remember each other. However, that's unlikely to stop the writers if they want to bring her back.