My Favorite TOS Show

The Galileo Seven
This one is my favorite for the following reasons:

The interaction between the characters (Mainly Spock, McCoy, and Scotty).
Scotty is asked to push the limits of his abilities to get the shuttle craft back in orbit, within time constraints. He overcomes almost insurmountable odds in his endevor.
McCoy keeps offering his 'human' advise to Spock, who 'logically' refuses to listen, prompting more advise, and a more animated McCoy.
Spock keeps 'logically' plugging away at the problem, but his logic seems to be challenged at every corner, not only by the other crewmembers, but by the ape-men attacking them.
Spock has to learn the lesson, that logic without considering the human equation will cause disasterous results.
The crewmembers, even though disgusted with Spock, show absolute dedication to him by risking their lives for him, when he gets caught behind a rock, despite his orders to them to leave him behind.
At the end, Spock out of desparation, 'logically' makes the decision to jettison and ignite the fuel tanks in an attempt to make themselves visible to a, more than likely, gone Enterprise.
Kirk, all the while, displays his commitment to the lost crewmembers, by battling time, and the High Commissioner, to use every last second available to find them. "I intend to continue the search till the very last second, by candlelight if necessary."