Since I saw the thread title change, I've been watching old DH scenes and episodes trying to nail down a definitive answer...and it's tough! There were so many fantastic episodes that it's hard to whittle it down to a single top episode.
7x19, The Lies Ill-Concealed is probably my favourite as it explores Bree's and Gabby's friendship in greater depth. The pineapple upsidedown cake scene is classic.
Franklin’s music profoundly touched and changed the world, because over and over it offered that bridge to salvation, to freedom.