I have been watching a lot of original Star Trek lately, and I think I have finally selected which episode is the worst.
And my choice was not the Abraham Lincoln episode, nor was it "And the children shall lead", nor was it "Miri".
It is episode 75 "The way to Eden", where a bunch of hippy protesters take over the enterprise. Never was there another episode of the show that felt so incredibly dated as that one, and it had like SIX songs, which was more than too much in my opinion.
Worst Next Generation Episode? "I, Borg", the one where their "ethics" keep them from defeating the Borg in one fell swoop, and this is the episode in which the Borg cease to be scary. They went from invulnerable zombie hive minds, to little Johnny Depp looking teenagers.
Deep Space Nine? Hmmm, the writing was a lot better on this show than the previous ones, although I had a distinct dislike for episodes that centered around Major Kira. My largest beef with this show was how Kira's past kept getting more and more complicated and unbelievable. The best episodes were the ones that centered around the Ferengi or the Klingons. I can't recall a single episode that stuck out as "worst" though.
I never really watched the other shows, so I have no worst episode for those.