Which Classic Doctor Who Episode should you buy on DVD?

If you were going to buy 1 story on DVD I would recommend The Caves of Androzani. A brilliant story starring Peter Davison as the Doctor, it is very fast paced and the tension mounts throughout the 4 episodes. It is truly a classic and should be seen as a definitive purchase.

Other alternatives are The Talons of Weing Chaing (Tom Baker) and Inferno (Jon Pertwee)