I would pick (times on this are rough guesstimates):

The Daleks (2 1/2 hours)
Marco Polo (2 1/2 hours)
The Invasion (2 1/2 hours)
The Daemons (2 hours)
Inferno (3 hours)
The Green Death (2 hours)
Robot (2 hours)
Pyramids of Mars (2 hours)
Genesis of the Daleks (2 hours)
Deadly Assassin (2 hours)
Talons of Weng-Chiang (3 hours)
The Stones of Blood (2 hours)
City of Death (2 hours)
Shada (2 1/2 hours)
State of Decay (2 hours)
The Curse of Fatal Death (1/2 hour)