Picking one is nearly impossible. I voted for casual content because it's the one closest to my heart, although Legion has done pretty well so far with world quests.
- I can pop an automatic queue for nearly everything !
I have no idea why Blizzard insists on making Normal+ raids non-queuable and LFR braindead and unrewarding. I like challenges, but here's the deal - I'm not very sociable and dislike forming/joining manual groups. I did A11 and A12 yesterday and that was some of the best fun I've had in a while with "LFR", while getting nice 250 loot too.
- "Timewalking" is activated by default. No idea why Blizzard doesn't do this as a permanent fixture like FFXIV does. I love being able to run all dungeons at 60 and help out lowbies with FATEs whlie still having it be relevant and not faceroll.
- The variety of glamour. It could do with being a lot more practical though. Just fuse the cool FFXIV skins with Legion's transmog system and it would be literally fucking perfect.
- Housing !
- Soundtrack of course, as mentioned by everyone else.