Pure personal preference. Depends on where the shooter grips the cue, how long their arms are... etc. Some shooters like a forward balanced cue others prefer more butt heavy. There is no standard "range" but in my experience 19 to 20+ would be considered forward balanced and 18 to 17- is usually considered butt heavy by the people I've talked with. But I have seen cues outside these ranges.
Most production cues I've measured are in the 17-19" area.