Beating Titan HM > Beating T5 > Beating T13 > Beating T9

(in that order)

At least those things felt the best to do - the original Relic quest was probably the most fulfilling quest I've done in the game, so I can understand why those that invested in all the other bits of it feel like that was a big accomplishment for them. Raiding was fun, especially early on, so beating T5 was a fantastic thing when I finally got a group to down it with. T13 was more of a "thank god that's done", and then T9 just didn't feel that great since I didn't raid for all of SCoB when it was relevant.

Hopefully there's more worthwhile fun quests in 3.0 that will leave me with good memories like the Relic/T5 did.