Rose clearly has fans, and Martha has her fair share of fans as well. Donna’s character is not as well liked so far, but Catherine Tate who plays her is very well liked and we will get a better taste of what she is like as the Doctor’s companion after series 4 begins. Donna’s popularity as a companion could very well grow before Rose returns. But with all three characters on the show at the same time it is very likely that at least one of these character are not going to have enough to do.
The question is who will fade to the background during these episodes and what companion out of the three will ultimately outlast the others? If Billie Piper wants to stay on past this season it will likely be her, but if Rose does not remain as a main character at least for the three specials following series 4 will Martha’s or Donna’s characters continue to be expanded?
Or… Since Kylie Minogue is rumored to want to return to Doctor Who in the future too, maybe there would be room for FOUR women traveling with the Doctor. Speaking of Kylie the band Fast Ood Rockers has released a very “Doctorin’ the Tardis” like song called “Song 4 Kylie: ...I'm In Love (With A Girl In A Time Machine)”. You can listen to it by clicking the play button to the right!