Nighthold, no question. I loved everything about it.
The bosses were great, plus there was the spicy bit of payback on Krosus and Guldan for the Broken Shore.
I also felt really, really powerful in there. I had gotten my two BIS legendaries by this point, and I actually got my 4-set during the first week it opened (my guildmates hated me for that).
Also, Suramar is easily my favorite zone in the game, and an entire raid based on it’s architecture is just an immediate shortcut to being loved by me.
And the cherry on top of it all, I was able to make many, many puns based on the bosses every night we were there. I told SO many dad jokes and induced SO much groaning from my guildies in there.
And the best part? I never DID end up getting either of mounts from there. Now, that sounds like a bad thing, right? Wrong. That just means that now, I can run it over and over again, and nab all of the amazing transmogs that place can provide on all my alts.
I can’t wait until I can solo-farm it.