Battle for Darrowshire had me tear up irl and feel extra heroic at the same time. In that sense it is very similar to the quest in Baldur’s Gate 2 involving a ghost of a halfling child.
Linken’s quest had me utterly confused, since when I did it for the first time in Vanilla, I’ve had literally never heard of Legend of Zelda or the Link character.
Surprisingly, nothing in particular stands out in TBC, but in Wrath I was especially impressed by the quest where you fight your future and past selves, and the one where you fetch A’dal from Shattrath to ressurect a common Alliance soldier who died fighting the Scourge. Oh and one remark in NPC idle dialogue stuck with me. It’s two soldiers talking in an Alliance base underneath newly returned Naxxramas I think in Dragonblight (?), and one of them goes, and I’m paraphrasing “Dude don’t worry, we gonna be just fine, I hear they are sending an entire platoon of Hands of A’dal outta Outland, they will make short wotk of all the undead here”. And that we did.