I'm going to ignore the core 3, because those are pretty important. They all have some issues, but they are also the framework for the game we love. I'm also going to only including books I've actually read (I never read HotDQ, because I've heard such terrible things about it)
Favorite: XGtE, because it was a massive crunch release for both players and DMs at the right time for such material to be added to the game.
Honorable Mention: GoS, because I love Greyhawk and it does a good job capturing the feeling of it. Saltmarsh is exceptionally interesting, and I already liked several of the adventures, plus it gave greate suggestions on how to incoporate TftYP adventures.
Worst: GGtR, because I'm just not that interested in the setting. Most of the crunch didn't seem very portable to my setting, so I really have no use for it at all.