People are starting to make this difficult for me.
I love "The Jem'hadar" and regard it as one of the pivot points of the series, where the show did something it couldn't just take back in the next episode. Seriously, the first time I saw it, when the episode ended I was left with a total sense of "Well, they're screwed."
"Way of the Warrior" brings in Worf and has the kind of space battles never seen in
Star Trek to this point (and one of two times we see DS9's become capable of putting up an actual fight).
I may draw some fire for this, but I'm going to give a point to "Duet". It's a great episode, don't get me wrong. But if it never existed, we wouldn't miss it because it doesn't have explicit arc storytelling (Kira's development, yes). It sets up an awesome Cardassian who gets killed at the end of the episode (justfiably?). In some ways I feel Legate Ghemor is ultimately a stand-in for Marritza, or an instance of what he could have been.
Duet - 1
Necessary Evil - 1
The Jem'Hadar - 3
Improbable Cause - 0
The Die is Cast - 0
The Way of the Warrior - 2
In Purgatory's Shadow - 0
A Time to Stand - 0
Far Beyond the Stars - 0
Tacking into the Wind - 0
The Changing Face of Evil - 1