The Changing Face of Evil is the big moment when Damar snaps and gets his rebellion going; the Defiant is heart-breakingly destroyed in battle; and Winn finds out that she has been sleeping with Dukat, though the accidental death of Solbor means his blood reveals the Kosst Amojan to Winn.
Tacking into the Wind is where things come to a head with Worf and Gowron, leading to Gowron's death, and Martok as the new leader. Worf and Ezri have a frank discussion about the Klingon Empire; Damar kills Russot when they are on-board a Jem'Hadar fighter; Bashir does his best to find out more information about the Changeling illness, but is stonewalled at each turn; finally, we find out Odo has developed the illness very quickly for all of the shape-shifting he has been doing for the resistance.
They're both good episodes, but Tacking in the Wind probably has more meat.