1-60 is usually almost 100% afk (Some toons it is, other it glitches on certain quests or for no reason)
60-80 is almost 100%
80-85 needs help with a number of quests, specially ones where it has to use an item on an elite rather then try kill it and fail so keep an eye out.
85-90 is pretty glitchy, generally only my blood DK's can do it without dying heaps.