TATV gets my vote because everybody is wildly out of character and there are too many plot holes for the story to make sense, even if you're drunk.
But if I use this very sensible criterion:
To me, only Precious Cargo and that TNG comeback tour deserve their place on the list. Yes, even Extinction had at least one moment I liked... namely Archer's dream where sees his non-mutated self, wakes up and describes seeing his "home" and his "people".
I'd have to go with
Marauders (reaching the opposite conclusion from
ChrisP) because I cannot think of a single scene I would stop and watch in that episode. I realized in that "special moments" thread we had going that every other ep on the list has at least one: the "tribunal" in
Precious Cargo, the "What the hell do we do with these people" debate in
Terra Nova, the "We think you may indeed be crazy, Captain" conversation in
Rogue Planet, Porthos' surgery in
ANIS (actually I like that episode as a whole), the pre-speech scene and montage in
TATV. But
Marauders, I can't think of even one.
Doh. I didn't realize until too late that I could have voted for two. Sorry.
TATV and
Marauders.