If you just want the FoTM, then you're probably looking at Pally tank and 3x BM Hunter DPS. Healer has more choise, but I guess the top ones are Shaman or Monk. Whether this will be the same for Shadowlands...


But as JG said: You can get away with a more compositions than before if you're not worried about getting every last bit of performance out of the group, so classes that you are familiar with and enjoy are a fair pick. And unless you're trying to push the absolute highest Mythic+ keys you possibly can, I would not worry about it. For normals, heroics and baseline mythic dungeons most teams will do fine.