https://io9.com/the-top-100-star-trek-episodes-of-all-time-1641565699
Lists like those tend to bug me since it's so subjective. Tons of things I could complain abut, but who'd listen. Instead I counted how many I could identify just from the picture. Got 72, including a couple of tricky ones.
And just to provide something to talk about, the top of each series:
TOS Balance of Terror (1), City on the Edge of Forever, Trouble with Tribbles
TNG Best of Both Worlds (2), Darmok, Inner Light
DS9 The Visitor (4), In the Pale Moonlight, Far Beyond the Stars
VOY Equinox (23), Year of Hell, The Void
ENT Twilight (33), In a Mirror Darkly, Dear Doctor
I'm in the CotEoF is the best ST has done camp, so I would have put it first in TOS, at least. Balance of Terror is a top 10 episode, but hardly the best of all series. Tribbles is overrated.
Thought BoBW sucked, suffering the same problem as almost all 2-part TNG episodes. Thought Darmk was overrated, as well. Inner Light is damn fine work, though.
I've got no problem at all with the DS9 list, although I think FBtS sucks, honestly. Good premise executed poorly due largely to the acting.
Equinox and Year of Hell are both good episodes. The latter might make my top 3, not sure. Timeless definitely would have, and probably Blink of an Eye; awesome premise.
All three of the ENT episodes are pretty good, although I have no idea how I'd rank them amongst the series. What I do know is that Similitude would top the list and didn't even make their 100.