Heart of Stone, DS9 3
Here is a terrific episode where you have not one but two terrific stories happening at once. Major Kira is trapped with an expanding rock formation trapping her to her doom, regardless of how Odo tries to help. Nog comes out of the closet and announces that he wants to be the first Ferengi in Starfleet. The end of the episode represents real, unexpected growth for all of the characters. This is a show firing on all the thrusters.