This is a decent entry in the innumerable series of puff pieces for Doctor Who. It gives an overview of the people who have traveled with the Doctor over the last half century and tries to figure out what these people have in common.
Although the piece has an air of overwhelming simplicity to it and seems to talk down to its audience, it is strengthened considerably by Peter Davison, who played the Fifth Doctor, and has maintained amiable relations with the current production staff (he has taken a continuing role in their reworking of scripts from LAW & ORDER for its UK version). His slightly quizzical handling of compère duties improves it, as do clips of his interviewing other actors who have played the Doctor and companions in the past.
As for the central question, who was the best companion, for me it was Ace, the bomb-wielding assistant of Seventh Doctor Sylvester McCoy.