4. Kryten Red Dwarf
The Doctor hasnt had a robot on-board since he gave K-9 away to Sarah Jane Smith. It would be good to see him travelling with another one, and who better than Kryten? Unlike most robots, hes managed to override his programming, with help from friend and last surviving human, Dave Lister, meaning that hes able to lie, insult people and express negative emotions without exploding. This, of course, would be beneficial if he was travelling with the Doctor. Every companion needs to be able to lie; it gets them out of danger and keeps up the morale of those they are fighting to protect. They also need to be able to think creatively and defy orders given to them when they think that they can help. As Krytens obedience programmes have been destroyed, he no longer needs to follow orders but of course, he still can. Since he gained the ability to think for himself, Kryten has been able to better himself; becoming an expert in science. He may not be quite up the same standards as the Doctor, but should the companion ever be? In any case, hed be able to offer some help and wouldnt mind doing the menial, serving tasks if he should have to.