Web and its not even close.
I love how Web on the surface is just a straight forward, fun monster story, yet when you stop and think about it, its really quite a mad mash of different things.
You have Yeti's from the Himalaya's, a Lovecraftian disembodied spirit from another universe, robots, a guy from the Highlands in the 17th century, a girl from the 19th century, all thrown together in 1960s London!
That was what DW always did best IMO. Merge different genres and bring characters that could never be together in any other work of fiction together.
Added to that Web has some of the best action sequences of all time, like the Yeti attack on covent gardens.
I also really liked Travers daughter. She was smart, brave and useful to the Doctor. Its a shame she wasn't brought back for the Invasion. Had they done that, then she could have been brought back for Pertwee's first season. As much as I like Liz, she might have been better.
(Though Patrick Troughton seemed to fancy her LOL. It obviously wasn't in the script, but you can tell in his performance. They'd have had to have nipped that in the bud on screen.)