DS9 - There are some pretty "modern" episodes here which makes the series more relevant, the Bell riots, the bar union episode, Pale moonlight(adventurism for the greater good), The Maquis arc, the changelings on Earth episode(9/11 reaction prediction) and a few more.

But there are some very silly and bad episodes too, I think the whole Bajoran religion can be a hit or miss. Gul Dukat is sometimes very creepy, Odo is a fascist(and that is ok) while the show doesn't realy embrace that("we can fix him" trope), the Ferengi episodes are fun but also shallow imo.

But I'd just give an edge to DS9 because the great episodes are more relevant and based on real world conflicts while TNG tends to be a bit detached and optimistic.

TNG- TNG S3-S7 overall manages to be pretty clean and principled imo. Of course from an entertainment POV some episodes are just ok, but there are some strong classics here, the Picard torture, Measure of a Man, Inner light, Darmok, Unification.

The biggest leftist problem with TNG would be a couple of specific episodes where the writers lacked self awareness and in general the establishment and then misuse of the Prime Directive.

There are controversial episodes like the Riker trans/gay sex episode, the Barclay episode, some horrible S1-2 episodes.

TOS is dated but was also quite bold at the time when dealing with race and equality issues. These days TOS doesn't have much to say because we take a lot of things for granted but credit should be given to TOS for the historical context. There are some pretty insane episodes here too but I think the balance is overall positive.

VOY-ENT both are quite unremarkable, they are not terrible series just average with few great episodes and pretty much nothing else. Enterprise had some unspeakable mistakes, the Phlox curing diseases is interfering with evolution nonsense is just way too much. I realy recommend SFDebreis review of Dear Doctor Realy as much as I hate nuTrek I think even Kurtzman would struggle to do something as shit as this.

There are some good storytelling moments from S3 onwards but it is not realy relevant to real world politics imo. I still recommend watching it because it is far better than STD-Picard, but it is not perfect.

Voyager has so many shit episodes, a few particularly bad ones like the Chekotay tribe was created by smart white males aliens. I point to another SFDebris review of Tattoo. but I struggle to think of any politicaly relevant Voyager episode. They fight nazis once so there is that.