It all depends on what you find inspirational, I guess. I find the characters' journeys on DS9 to be the most inspirational writing in Trek. I like TNG and TOS a lot, but the way DS9 took what had been done on those shows and challenged it, struggled with it, rejected some of it... It's a lot healthier, really, as a way of looking at the world than some of what TNG had to say. I do love TNG, and there are some inspiring episodes, no doubt. But on the whole, DS9 is the story I tend to go back to (speaking of the overall fabric of the show). TOS is more of an acquired taste to me, as it was already decades-old before I watched any of it.