The winner with 7 out of 28 votes (25%) is...
The Die is Cast
Here is a wonderful extra about that episode from the DVDs with commentary from director, David Livingston:
And for all of you battle scene junkies, here are some heart-pounding moments from the episode:
Some interesting facts from Memory Alpha
• This episode was the first with Ira Steven Behr as Executive Producer. One of the major changes he made to the series was that action sequences, specifically space battles, had to be shown on-screen more often and not just referred to, as TNG had repeatedly done. As the episode budget of DS9 shows could now accommodate more extensive battle sequences than TNG could do during its series run, starship fights became more commonplace in later seasons – especially during major Dominion War episodes. This particular episode marks the first signs of this change, as it features the biggest on-screen battle in Star Trekhistory up to that point (the Battle of the Omarion Nebula).
• Visual effects supervisor Gary Hutzel was instructed to come up with a way to do the battle scene without going over-budget. His solution was to create transparencies of the models of the Romulan warbirds and theCardassian ships, and to use those transparencies in the background. Coupled with the fact that they were in the background, Hutzel ensured that the camera never lingered on one of them too long, so as to ensure viewers didn't spot the effect. (Star Trek: Deep Space Nine Companion)
• The shot where the USS Defiant destroys a Jem'Hadar fighter and then flies through the debris took 4 days to film. (Deep Space Nine Chronicles)
• Writer Ronald D. Moore, director David Livingston, composer Dennis McCarthy and actor Rene Auberjonois were all extremely proud of the scene where Garak tortures Odo. Livingston says, "I think the scene is the best in the episode. It's very intense, very dramatic, very powerful;" McCarthy explains, "I had to express the horror of what Garak was doing to Odo and yet still put some shred of humanity into the music to show that Garak was suffering too, because Garak was having a hard time doing this. It was an opportunity to get very atonal musically. I don't believe that we ever heard a major chord on that show;" and Auberjonois notes, "I felt like some character from King Lear. The acting method I used was very Shakespearian." (Star Trek: Deep Space Nine Companion)
• This episode is the halfway point of Star Trek's current run of 726 episodes.
• This was the first Star Trek episode to have a two-parter with different names.