I voted for "Shuttlepod One," but it was a hard choice. For me, that episode ties with "Strange New World," "The Andorian Incident," and "Breaking the Ice." I like each of them for different reasons.
"Shuttlepod One" is the episode that I might use to introduce people to Ent for the first time, and if any of the season one episodes were going to get an Emmy, I think it would have been that one. The actors gave amazing performances, and we gain fascinating insights into the characters. In the beginning Trip doesn't want to give up hope (not out loud, at least), while Malcolm expects the worst. But then as their seeming demise draws closer, they reverse positions and Trip is willing to sacrifice himself to save Malcolm, while Malcolm would prefer to cling to the last bit of hope that somehow they might both make it out alive. And the expression on Trip's face when he realizes they will run out of air before
Enterprise reaches them - WOW! What acting!
"Strange New World" is the episode that first made me sit up and take notice of Trip, and, even more than anything in "Broken Bow," it made me start thinking about shipping Trip and T'Pol. I don't know what it says about me psychologically, but I really find crazy, paranoid Trip pretty sexy.
"The Andorian Incident" has Shran. Enough said.
"Breaking the Ice" is the episode where Trip realizes there's a whole lot more to T'Pol than just a hard, cold Vulcan shell, and T'Pol realizes Trip is someone she can trust (at least a little). The pecan pie at the end is a great foretaste of what's to come.