It may be irrational of me, but human beings are my favorite species.
The beginning of the Hinchcliffe era - the Fourth Doctor's first story Robot feels much more like a Jon Pertwee adventure - and the true relaunch of Doctor Who into space after the predominantly Earth-based adventures of the Third Doctor. This Doctor takes to stars with Sarah and Harry and finds humanity in cryogenic suspension and an alien threat stalking the air shafts. This story has a great Alien-style vibe to it. There is a scene in which Sarah finds herself stuck in a shaft that is filled with tension and claustrophobia. It also shows the Doctor at his most cunning as he seeks to stop the Wirryn from killing the crew of the ark. The effects might not stand up to today's standard but the tension and drama more than make up for it. A story that has been redone in some form more than once, this remains a favourite of both Steven Moffat and Russell T Davies and it's easy to see why.