For me, it’s Guns, Love and Tentacles, and it’s actually become my favorite campaign DLC in the series.
I loved the enemy design and mechanics (wolvens, the Bonded, krich and even the Frostbiters were intriguing, despite being COV reskins), the level design and map aesthetics (the Cankerwood is one of the best looking maps in the franchise, in my opinion) and also all the Lovecraftian inspirations and references (despite being part of BL3, I think they were handled quite well, almost never going in an excessively goofy direction).
Xylourgos is really beautiful, each map feels consistent but distinct (unlike on Eden-6, for example). It also felt plausibly lived in, with all the fish nets, the posters inside the Lodge or the paintings inside the Archives. I wish I could see more of it!
It also had the best new NPC cast across the board compared to the others (Eista, Mancubus and Burton), while still featuring previous characters in (more or less) meaningful ways (Hammerlock, Wainwright, Claptrap, Gaige and Deathtrap).
The antagonists were good enough, as was the music.
It also had a lot of attention to detail: turrets built by Frostbiter tinks have a unique model compared to the base game, creature head trophies inside the Lodge respect their actual size, the joke-telling fish were hysterical and all the variety and personality shown by all lootable objects were STELLAR. There isn’t a time in which I open a Bonded red chest (the red, tentacled ones that almost look alive) without carefully listening and looking at its beautiful animations.
The weak aspect, in my opinion, are actually the guns (which was to be expected, since it was developed by Gearbox’s Quebec studio, the same that made Fight For Sanctuary). Apart from a few gems (like the 7th Sense) they are either unbalanced or shameless copycats of main game items.