All characters come with three perks (teachables) that can be unlocked for other characters when prestiging them (after level 50). Killers also have a unique powers.

Indeed some killers are less popular, right now one of the most hated ones is Skull Merchant. She was highly problematic and already got a rework but still most people don’t like her. Knight is another killer who doesn’t get much love.

Other than those, there are always people who like or don’t like to play against certain killers. Often it’s more a matter of how they are played and in some cases how good they are - a top tier Nurse or Blight can be miserable to play against, but I find a „normal“ Blight pretty fun face. Same for Nurse though a „decent“ Nurse is tough to find. Most are either bad and you can run circles around them, or Godlike.

You can play with/against anyone, in public as well as private matches, they don’t have to own the same character.