I think Knock Off should be a primary option because of its general utility against bulky/defensively minded teams that enjoy leftovers. Even many offensive teams use Life Orbs and Choice Bands to guarantee crucial 2HKOs, and taking them off means that threats can be stalled and phazed easier. For example:
607 Atk vs 368 Def & 420 HP (120 Base Power): 213 - 252 (50.71% - 60.00%)
A Choice Band Salamence/Dragonite/Tyranitar, all common switch-ins to Tentacruel (well, Dragonite isn't common :)), using Outrage/Aqua Tail on a 252/252 Hippowdon. It 2HKOs, unless the band is knocked off, resulting in
405 Atk vs 368 Def & 420 HP (120 Base Power): 142 - 168 (33.81% - 40.00%)
which is easy enough to recover on and phaze away. It could be argued that you could not use Knock Off and instead switch to Skarmory after Hippo takes an Outrage, but then Hippowdon has sustained a good deal of damage, which is unfortunate, since he is often one of the most valuable parts of a stall team, and should be kept health just in case a Lucario shows up after Gengar Shadow Balled a Rotom predicting a Focus Blast.
Gyarados needs a Life Orb for the 2HKO on Celebi. If it is removed, it can easily be stalled out.
In short, it depends on your team: if you have a lot of instant recovery, like Hippo, Skarm, and Celebi, Knock Off is probably a solid option. If instead you are using stuff like Swampert and Forry and seeking to directly counter offensive threats, you could probably use Sludge Bomb to ensure your defensive counter can finish off the Gyarados or whatever.