My favorite episode is Blink of an Eye
. I loved the concept of seeing a civilization growing right in front of them, sending the Doctor down to the surface for three years, and how cultured he was when he came back. The race that wanted to blow the skyship out of the sky, and evolves to a technical ability beyond that of our Intrepid starship. Fantastic episode.
I also relate it to the TNG episode Inner Light
, as a previous poster mentioned above.