We went with Balance of Terror, and mission accomplished! He loved it! Thanks so much, everyone! While we ran out of time to watch a second episode, he is eagerly awaiting the next one. Corbomite or Tribbles will be next on the list, and then I'll set him loose to explore on his own. This is really awesome - thanks a million times, guys!
I'm glad this thread got bumped so I got to see it.
I'm curious how the rest of this story went down. It seems to me that someone could like Balance and Corbomite, and not like seasons two and three, what with the changes of producers etc.