Those that aren't repeatable and complete more or less by accident while doing stuff (like events) in the area are my favorites.

Inititally GW2 wasn't even supposed to have Hearts. They were a last minute addition because ArenaNet feared that people wouldn't have enough direction otherwise.

Nowadays Collections are often used as a replacement for Quests. Sometimes with all the annoyances of traditional questing, i. e. you have to constantly go back to the quest giver (Gorrik for the Skycale collection for example) in order to progress. Some of those collections have pointers (marked NPCs), but many have not. Even worse, finding certain items in the game does not count for their corresponding collection, unless you have it unlocked already. Terrible!

I think ArenaNet should stop abusing collections and add a dedicated questing system (outside of the personal story), since it is a great and easy way to add content to already existing zones, e. g. I really like Scavenger Hunts.

But please don't let us fetch and hand in quests like in Vanilla WoW. Dunno, if anybody here played WildStar, since GW2 could do this similarly by using existing systems like Mail and the commander's Communicator. And please automatically unlock quests (collections) as soon as we bump into any of the objectives by accident (like in WildStar).

Oh, the Nostalgia ... I even have a Mech named Eldan Construct.