"Of course… who else?"
I feel I ought to explain why I put Donna in the room. Now I know that Donna being in there is very unlikely, but I really don’t think it’s himself either. Amy saw herself in her own room too, but it wasn’t so much herself she was afraid of, but her fear of abandonment by the Doctor.
So what is the Doctor’s greatest fear? I think that it’s failure, that one day he won’t be clever enough or quick enough and the people closest to him will die. After he sees his own room, we see him visibly affected, and he seems to finally own up to the fact that he’s ruining Amy’s life, that he’s leading her by the hand to her death just because he wanted to be admired.
So I put Donna in that room because out of all the companions the Doctor’s ever had, Donna is the one that he failed that most, that he killed by his own hand. She represents his greatest achievements (helping Donna to mature and become a better person, to help her realise her potential and her brilliance) but also his ultimate failures (that he’s never going to be good for his companions, that his hubris will ruin their lives). He can make amendments of course, he’s got a time machine after all, but is it any consolation? Rose gets a job at Torchwood and Ten2, but she’s stranded in an alternate universe. Martha has a job at UNIT and Mickey, but what has her family been through? Donna gets to win the lottery, but she’ll never believe that she has any self worth or potential.
At the end of the day, his companions may have the time of their lives, but at what cost?