How useful are the exotic languages?

I’ve chosen the Haunted One background for my new half-orc blood hunter. I get to pick an exotic language (Abyssal, Celestial, Deep Speech, Draconic, Infernal, Primordial, Sylvan, or Undercommon), but other than Draconic (which I’ve only ever used as a dragonborn, to talk privately with other members of my party), I have never come across any of them before.

How often do you encounter an NPC that uses them, and how likely is it that I’d end up using any of them? Do any lend themselves to being more useful than any others?

I’m yet to flesh out my backstory, perhaps that will guide my choice, but before I do that it would be good to know more about the languages.