Hell and Inferno. Perhaps even in nightmare, but those rare/champ packs are usually killable fresh from normal. So take heed of aggroing packs that you can't beat and then portaling back. They apparently will follow you if they can.
HC players...
Act1: Inn
Act2: Main camp is safe
Act3: "Down stairs" is safe barring the event there.
Act4: Main camp is safe
