For Next Generation, I think I would have put “The Inner Light” on the list instead of “Yesterday’s Enterprise”. As others have said, both SG-1 and Babylon 5 should be represented on that list. The Quantum Leap episode “Good Night, Dear Heart” should be a contender. I don’t count Buffy the Vampire Slayer as science fiction, unless you want to open the door to fantasy and superhero shows. I think Lost is iffy as science fiction and it had some excellent episodes but I’m not sure I would consider “The Constant” the best. My tastes are somewhat quirky so I’ll leave it at that.
I loved Inner Light, but Yesterdays Enterprise is my favorite for sure