My vote goes to DS9 season 2 which is severely underrated. Althouth I like the latter half of DS9 more – mainly because it had Worf in it, and Worf is the best {{:-) – season 2 lay the foundation for DS9’s later success.

The whole season is a huge step up from season 1 which often felt like TNG on a space station. In season 2 the writers began to really try out new things. It starts with a never-before-done 3-part episode, then does some more great world-building in “Cardassians” and “Necessary Evil”, then slowly builds up a mysterious force in the Gamma Quadrant by the name of “the Dominion”, then achieves the feat of making Bashir likeable in “Armageddon Game” upon which his friendship with O’Brien is built, then does a couple of standalone highlights like “Whispers” and “Blood Oath” (in which Kor, Koloth and Kang return! which in today’s crossover-ridden landscape would be just a footnote but back then it was a huge deal), then lays the foundation for the Maquis on Voyager and also does more with the Maquis then Voyager ever will do, oh and in the same episode spells out the show’s leitmotif “it’s easy to be a saint in paradise”, …

… and we’re still not done yet because the rest of the season is a total banger: “The Wire” is a trip into Garak’s psyche, “Crossover” brings back the mirror universe, “The Collaborator” is a big step in making Kai Winn one of the show’s main antagonists, “Tribunal” is the OG O’Brien-must-suffer episode, and “The Jem’Hadar” introduces the Dominion literally with a huge bang by blowing up a Galaxy Class ship. You know, the ship class that we just spend 7 years with and which escaped countless foes unscathed.

Seriously, never skip season 2 on your re-watch. Don’t listen to anyone who says that “DS9 only gets good once the Defiant shows up”. No no no. This is the real deal.