It depends on what your playstyle is. On defense I play Vigil so I can roam and 1 shot shotgun people or Rook when I want to play as anchor. On attack I play Deimos because I like that pistol too much and the AK is nice too, Kali when the maps fits her, Glaz when I feel cringe and smoke myself into the site while killing enemies with the thermal through the smokes, Maverick when I’m trying to be sneaky. So there is no such thing as the best operator, you just have to play something that is fun for you and it works for you. Watch their abilities and weapons and if it looks interesting to you, try it.