Probably a minority choice, but I really like the Phiarlin Carnie chain. Partyrashers is an easy #1, Big Top #2, and I'd have to put Snitch and Problem as a tie for 3rd.
Otherwise the second half of Sorrowdusk is nostalgic (my first pack I bought), and that chain probably can be considered a single quest due to the repetitious dungeon(s).
Raid...I'm pretty fond of the entire Subterrane, still that one area that remains mostly mysterious even though I've been through it a bunch of times. Whatever those floating meteor things are, they really woke me up my first run through there...and the raids themselves are fun.