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).
A well developed quest system also has it's perks. I really enjoyed picking up 20 quests, doing them for 1-2h hours and cashing them all in at once. But it's always annoying if there is a lot of running around without anything to do in between included.
I would not call the heart system perfekt or great, because there are a lot of hearts, that are completing very slow or require tedious tasks. It's also annoying that progress is not shared in a group. But the system is unique and most tasks are fun.
That's kinda surprising, since GW2 doesn't actually have quests (outside of Core, Expansion and Living World story). I played quite a few MMOs and I think ESO's and Runescape's side (story) quests are pretty good. WildStar had the best questing interface which avoided unlocking, fetching and handing in quests by using a communicator device. It had some nice (zone/story) quests, too, but overall there were too many (boring) quests which you mainly did to grind XP.
I remember when GW2 came out, I was trying to explain to a friend that there wasn’t the traditional kill x / collect x in the game. He just couldn’t understand how it worked and kept saying how was he supposed to know where to go, if there was no NPCs telling him 😂
The ones that weren't gutted that much by new player experience and in turn become idiot-proof ride, because some clown at arena got some serious telemetry in which he saw feeding cow with hay being "too confusing".
Any heart that has enough compatible events nearby that made pumping progress faster. And also these that aren't limited to one particular task (because of npe).
Although hearts are really well done in Guild Wars 2 I just don't like these type of quests in any game. I don't do hearts unless they accidentally complete during a meta or something.