The question I'm more interested in is "which game has your preferred dungeon/raid gameplay?" Since questing and killing mobs out in the fields to level is not that great in most mmos you play. Classes and by extension skill rotations, the fun parts are usually explored more in dungeons/raids.
I prefer XIV dungeons/raids. First I'll get out of the way that there are far fewer bosses in XIV. There are only 3 bosses per dungeon (I think 18-20 dungeons in the most recent expansion cycle), and a total of about 20 raid bosses for an entire expansion cycle, at two difficulties. The most recent expansion added 2 additional bosses at new highest difficulty. Dungeons are 4 player, raids are 8 player. I'll focus on talking about raid bosses, but a lot of this applies to dungeon bosses just to a lesser extent.
*edit* I also forgot to mention that there are 3 24-person raids per expansion. They are between LFR and Normal difficulty to compare to WoW, and include about 4 bosses per raid. Most of what I said here applies.
Each raid is just one boss basically, so you don't have to worry about wrangling a bunch of people for a long time, killing trash, or repeating content to get to the boss with the loot you need.
The theatrics of XIV bosses are way more impressive. Each raid boss has its own music and will have many custom animations and mechanics. Often they will have two phases with a dramatic phase transition. In the most recent expansion, the final boss of each dungeon is essentially a mini raid boss in terms of the custom attention they got from the developers.
Most mechanics in XIV share a common design language, so that you don't need to relearn every move for each encounter. For example, if you need to stack, the stack icon will be the same for every boss fight. This lets you focus on the few unique mechanics to the fight without relearning everything based on the new animations.
WoW raids rely a lot on improvisation and response due to the boss AI. In XIV, the boss mostly runs on a script with very few random elements. This means you focus more on learning and execution as opposed to adaptability. Some people like this, others don't.
Itemization for raiding in XIV is almost nonexistent. With few exceptions, you're grinding to get the item with higher item level and it will be your best in slot. Items do not have interesting active/passive abilities which meaningfully change your playstyle. There are also no talents. Your kit is your kit. If you want to play differently, you play a different Job/Class.
Rotations in XIV at level cap are comparable to WoW, but again have less of an improvisation element and more of an execution element. Some recent classes like Red Mage and Dancer buck this trend and have more proc-and-priority-based gameplay.
As a "mid-core" player, the lowest difficulty level in XIV is incredibly satisfying to me (Normal trials/Normal raids). 8 people must respect mechanics, but often one mistake for the entire group per minute is recoverable and the DPS checks are present but forgiving. Compare this to LFR mode where you don't pay attention. I would say it is also slightly harder than Normal mode WoW raids.
The next difficulty tier (EX Trial) is also very satisfying. You can PUG it, but not every PUG group will clear it and it may take you several full timers (1 hour) to learn the fight well enough to clear it. DPS checks are raised but still don't require top-10% execution.
The highest difficulty tiers (Savage and Ultimate) are mostly beyond my interest. I might clear the lowest level Savage raids each tier but I have never fully cleared.
My suspicion is that Mythic+ grinders and Mythic WoW raiders would find XIV's content too limited. Where it shines is for players that:
- value presentation/polish
- are bored by LFR but don't want to organize large groups of players
- don't mind the smaller amount of content in absolute terms
- want to jump into a fight and master it rather than worry about their gear choices.
