If you could choose only one to affect Imbued, which one?

I'd say : none of them.
But before answering, I'd like to know if the vampires themselves are aware of imbued existence ? Until now I guesses that most of them don't see anything surnatural when a human comes and intercept/defies them. They just see a foolish human and if something a bit surnatural happens, they simply think some other forces are at work, or maybe the human was just lucky... They dont' think about powers or virtues, because it's a bit out of their reach. Mehuselahs (players) do, but not their minions...

After a combat I'd understand a vampire who takes time to decapitate another vampire to make sure he never stands in his way again, but after dispatching a puny human who seems dead cold, why the need to stop and tear him apart ? After all, there's nothing to fear from an unlucky mortal bystander.
So Disarm and decapitate should not work on them simply because a vampire would not bother : what is dead is dead.

I agree, none of the above. If you are playing combat, you are already probably tearing up imbued. If you are playing light stealth on the other hand, you are screwed. I'd like Seduction, Mind Numb and, if I had to pick one from the list, Obedience, to affect the imbued. Not that they wouldn't just "React with Conviction" and cancel Mind Numb, but at least that's one less conviction for them. And then I'd want Diamond Thunderbolt to affect all allies. I'm so tired of getting allies stolen when I don't have a DI or crazy intercept.