Favorite: ITPM. But Duet, Necessary Evil, Purgatory/Inferno, Rocks & Shoals, Call to Arms and Sacrifice of Angels also get high marks from me.
For episodes that don't get mentioned incessantly, I also like In the Cards (which was well positioned as being the "last moment of normalcy" before things really got intense at the end of S5/beginning of S6) and the Odo & Weyoun story in Treachery, Faith and the Great River. And everything involving Kira, Damar, Garak and Odo in the final S7 story arc.
For episodes that don't get mentioned incessantly, I also like In the Cards (which was well positioned as being the "last moment of normalcy" before things really got intense at the end of S5/beginning of S6) and the Odo & Weyoun story in Treachery, Faith and the Great River. And everything involving Kira, Damar, Garak and Odo in the final S7 story arc.