no contest: "The Wounded" is the best Trek episode ever IMO.
It deals with far-reaching political intrigue, several very human and personal issues and heavy stuff like prejudice (I know Gene didn't like things like that, but I think it far more likely that humans will always harbor prejudices), and the lingering after effects of war, something that we often as a society shy away from.
It introduced the Cardassians, one of my favorite races.
It has the warden from Shawshank Redemption, that guy is money in the bank.
It was just about the first starring episode for Colm Meaney and he knocked it out of the park.
But most of all because of that scene between the two. They start singing and the camera just slowly pans around them, no cutting away. Then they stop and the song starts up very feint in the background music and you see Maxwell come to the realization of everything he's done and everything he is, just with a look. Man it makes the hair stand up on the back of your neck. That's just absolute perfection in drama, acting, writing, sound design, set design. Everything comes together in that scene.
And to top it off, Picard's "We'll be watching" to Gul Macet at the end. Picard ain't no fool.