BFA by far.
WoD was bad but at least the classes felt fine to play(3 charges of wings? YES PLS). Garrisons kinda fell flat but were easy gold making machines. The story was given up on for more work on Legion so RIP. All in all, yeah it was bad but I still enjoyed it.
BFA takes the piss. Beginning of the expansion? Ret felt like hot garbage and the azerite system made me nearly quit. Battle of Dazar'alor got better. Then the Rise of Azshara patch hit with the essence system on top of ranks for them and that never felt good to me.
Then the RNG hell that is 8.3 came out with corruption. Sure, now you can target ones you want but even still it's messed up when you look at your damage dealt and it looks like this for some classes:
Absolutely terrible story. So badly paced and just out there. "Hey we stopped Sargeras and he impaled the planet. We should probably heal that. OH NO WACKY SYLVANAS STARTED A WAR, BETTER FIGHT CAUSE WHY NOT. OH NO, N'ZOTH IS FINALLY HERE!" and then he just...dies in a kamehameha cinematic after so many small hints and nods about him being this super clever and cunning old god.
Oh, also the GCD thing. Still garbage. Glad Shadowlands is reverting some of it but it never should've happened in the first place. Same with the aoe target cap coming up soon. Can't wait...