From my experience, WoD quests award the most XP.
I think BFA had some nice quests, but then again if you ask me id say BFA had best everything
Wrath. Amazing Villain. Beautiful zones, Arthas made himself present in a lot of zones.
MoP for a very close second.
Worst I’d say is Legion.
Legion is my top pick with BfA second. I really loved the zone quests in Kul’tiras especially.
I liked WoD and Bfa - thought they were fun throughout (except S4 of Bfa)
The best questing for me happened in MoP, WoD and Legion.
Boy those were some good times! 