I voted WoD solely because of the way it started: with Garrosh escaping trial by traveling to an alternate Draenor at the behest of some crazy bronze drake who wanted to create an infinite Horde to rule the multiverse...and then killed the drake before we even got the expansion pre-launch event. If you removed that aspect and had WoD as a standalone story without the hurdles to make it feasible from a lore perspective, I think it would have been better. The ending of WoD left a lot to be desired (they really could've used more Iron Horde resisting Fel Horde and turning to the Horde/Alliance to sell the ending), but most of the story up until that was pretty good; there were a few instances that could've been improved upon, such as Ner'zhul's plot.
Shadowlands fits more cohesively into the Lore than WoD did, but the story has one big issue with it, and that's Sylvanas. At least Garrosh had the decency to take the back seat in WoD; Sylvanas remains front and center with nebulous motivations and an unsatisfying narrative arc. While her characterization is fine for a sideplot character, I'm getting really tired of her appearances after two expansions of significant plot relevance following one with two significant B-plots. I am also done with her "Name. A disparaging noun paired with a traumatic event." greetings with every NPC that confronts her. Her appearances have become too formulaic to be interesting.
Edit: While this is slightly off-topic, I feel it should be noted that the two proposed are not narratively the worst expansions of WoW. Both TBC and Cataclysm have greater narrative issues than either of the ones being polled about.