It depends on the quality and design rather than whether it has a digital or mechanical readout. There are good and bad scales in both categories.
The best indication of scale quality is consistency. Weigh yourself several times. A poor scale will read a different weight every time; a good one will read the same or very close every weighing. Another neglected area is choosing the wrong range. Scales are usually most accurate in the middle third of the range. If you weigh 100lbs than you shouldn't buy scales that go up to 450lbs. Likewise if you weight 300 lbs and buy scales that only go up to 350lbs they probably will not be accurate. Quality scales should last a long time. Kids seem to be the hardest on scales because they drop them, kick them around, and jump on them. Scales are precision instruments and do not take this kind of abuse very well.
If both digital and dial scale are good quality, which would be better to have? And I do have kids so I don't have to worry about that.