Healing is possibly the best role for raid leading from my experience. As tank, raid leading can be a little rougher to see what's going on around the room. I haven't done any raid leading as a ranged dps, though it would be a bit tougher to perform optimally while doing so. I've done quite a bit of raid leading as melee dps, but you do really suffer in personal performance while trying to spin your camera to keep an eye on all the action. It was a bit easier before Legion nerfed the camera max range. Given all 4 options though, I would definitely pick healing as the preferred role to handle all callouts.