Devil's Sight is boring and not that much more useful than regular darkvision in most campaigns. You can do the Devil's Sight darkness combo but i think that sounds better on paper than it actually plays in the game (impacts allies too much)
Unless you start as a variant human for the feat that would be my pick if chosing between those 2. Variant human and something like actor feat + at will disguise self is really fun - but not so much what you are planning for with your build.
Keep in mind as you get higher level you can trade out lower level invocations. So you won't always be stuck with either if something better comes along.
Hmm. I never thought about casting the darkness on the enemy for the darkness/devil sight combo. I always cast it on one of my own items and enjoy the benefits while not obstructing my allies except for very very rare situations.