The first two seasons are good and about equal in quality, but the third season is nicknamed the "Turd Season" for a reason.

TNG is best during the seasons Riker didn't shave off his beard.

And DS9 is best when Sisko shaved his head.

This hair principle is basically how I know whether to stop and watch an episode or just keep on turning the channel.

That episode is so amazingly bad that the Agony Booth selected it as a "Worst of Trek" episode.

Is that Roddenberry-level-subtlety for an allegory about workin' on some backed-up cheese that's turned to glue, and you end up with the big red ring imprinted on your upper thighs and ass?

There's an episode at one point where the ship loses power -- except for the holodeck. Apparently the holodeck has it's own power source, and it's incompatible with the other systems on the ship.

The worst part is, this isn't the worst scientific howler in the series. That goes to the whole concept in the first season that there's no water in the Delta Quadrant -- water is one of the most common substances in the universe. Just find a comet. Then there's the episode where they stop to mine deuterium -- deuterium being an isotope of hydrogen, not a freakin' mineral.

TOS is the correct answer.

This is a hard question for me. I grew up watching 'Voyager' so that series will always be fondly remembered, but now years later I have to say DS9 is the best written/acted out of the series - not to mention that if you don't count the theatrical films its the only series were I was able to get completely enraptured within the characters and their fates.