A friend and I were circlejerking about Star Trek for the millionth time and both of us think that DS9 is the best. He mentioned the episode of TNG with Bashir, and how he is just, like, super boring in that episode, and more or less denuded of all character by the writers. Siddig does a good job and puts his energy into the part, but on the page he's just pretty bland compared with the guy we know from DS9.

In taking a look at that episode, I think I figured out the main difference between TNG and DS9. This is my theory, anyway. In most TNG episodes, there is some kind of technical or cultural problem (Wesley strayed into the flowers, and now must die!). The characters on the Enterprise must then solve that problem before it is too late. There is almost no inter-personal conflict between them. They all like each other and work well together. And they don't really have any flaws (until Picard slaughters thousands of people as Locutus). The better episodes of TNG (I think) rely on interpersonal conflict rather than random arbitrary challenges. An episode like The Best of Both Worlds combines these: the crew has to fight the Borg while also fighting their own captain.

In DS9, in contrast, interpersonal conflicts drive most of the plots, and every character has some kind of "flaw" that the writers push as far as they can. Odo is fighting a war against his own people (and is also a fucking cop who executed Bajoran freedom fighters for the Cardassians!). Kira is trying to balance Bajor's freedom with its security needs in a dangerous Alpha Quadrant. Sisko is kind of into being a religious figure for an alien people, which flies in the face of the prime directive. He has to balance THREE or even four different duties: to the Bajorans, the Federation, his crew, and his son. Jake stays on the station, putting himself in a lot of danger, because he wants to be a writer. Nog is conflicted with his Ferengi family in joining the federation, and overcompensates for that by being obsessed with Red Squad, which almost gets him killed. Quark is a greedy businessman surrounded by communists who kind of just leave him alone and even help him out sometimes, which in the end makes him much less of a fucking asshole. O'Brien also has to balance family with work. Bashir is super smart but kind of alienating to his colleagues, and I've seen some people call him creepy, but even as a kid I thought he was really cool. Worf has a similar conflict to Odo: is he with his people or not? And Dax...Dax is just kind of there, a trans character, seemingly along with Odo, who as far as I can tell "chooses" to identify as male.

Every pre-2009 Trek series has good and bad episodes, but I would say that at least 95% of DS9's episodes are either good or great.