Sorry for the delay. Vacation, blue screen of death, yada yada yada...
Anyway, the winner with 6 out of 18 votes (33.33%) is:
Trials and Tribble-ations
There is a lot of technical info and interviews surrounding this episode due to its unique nature and the fact that it coincided with the 30th anniversary of Star Trek. I encourage you to check out all of the goodies on Memory Alpha if you haven't already:
The making-of is also out there on youtube. Here is part 1: