Mine is Grothmar Valley (episode number #1, titled Bound by Blood). Maybe it's nostalgia already, since in September 2019 world was like usual... Also, i really liked whole atmosphere of celebration, yet it was quite sinister from very beginning with all the accidents. The events of episode was happening behind our backs, we as Commander didn't really were in epicenter of them. Secondary, "The Metal Concert Meta" was something really unusual and cool, not your regular MMO meta event. I liked Ooze event as well. And in general there wasn't much events, but this fact added to calmer mood, storm on the horizon feel. Map was bigger also, unlike others we had it all in one package. Exploring it with rented Skyscale was easy, but i really loved last POI (had to view guides online and made party for it, but this was memorable). I think jp of Khan-Ur is only HUGE side thing i did from all episodes of Saga too.
Now, by no means i say rest of Saga is bad or something, especially i liked Visions of the Past, which takes place 2 in my list. But upcoming 2 episodes after the Bound by Blood was more usual stuff and with all the creepiness when you have to explore empty keep - wasn't very light. However i was kidding, that Bjora Marches is mine WotLK since i haven't played it originally. I had a blast in Whisper in the Dark honestly, but in old-school kill stuff/do quests manner.
And i havent played none Drizlewood Cascades yet, but spoiled myself for almost everything (waiting for VA).