Without a doubt, Heavensward.

Many little things were imperfect, but, at this time, Square Enix were giving things for all kind of players. The casual had dungeons or raid on an easy version, but, could still die and had to do some mecanics.

Extreme and Savage raids were for players who wanted a good challenge.

The big plus :
-Difficulty. In everything, even casual stuff, we could die. We need a stress in a game to be fun, not necessary Dark Soul kind of stress, and HW was still far from that, but it was not a braindead game.
-Difficuly on crafting and gatherer : Old players remember that we needed to farm some redscrip to buy talisman, that was enabling special nodes for a limited time. We needed to gather those to get special mats to craft the raid tier, or the crafting/gathering stuff. Also, each crafter had it's own crafted gear that way, same for gatherer. Those thing were harder to script in a bot, so, there was a lot less of unskilled crafter that uses stuff like plugins or bots to solve the crafting. The recipe were also really hard to HQ, especially without all HQ mats.
-Trinity : Healer were needed and had to heal, tanks needed an healer, and DPS had to dps to pass the dps check.
-Job complexity : They were fun. Think of the Dark Knight where you had to manage your mana to tank. No mana = bye bye tank. Machinist was also way more fun. Scholar had dots, cleric stance and many more attack spells. Summoner had a really nice rotation to play. Since ShB, playing a healer feels the same, and they are not really needed anymore. Their dps rotation is basicly spamming a button. They are now so boring to play, and have an heal kit way too strong for what the game challenge.
-Seasonal events were fun. Lots of mini game to farm to get your reward.
-Relic weapons. Probably one of the best set to do, yes, you need to work for it. Not just farm 1500 memoquartz and voila.

I'll stop here, that's my big plus that the game had back them. There is some low side, like for example this is the first expansion where sightseeing became.... boring. it was fun to do in ARR, and then, I really don't get why they keep doing it with this formula.