If you want to monitor your weight, any basic bathroom scale—dial or digital—that gives consistent readings is sufficient. The more fancy extras and the more stylish the look, the higher the price—but not necessarily the better the performance.
Test different models in the store. Set the scale on an even floor and weigh yourself several times to see if the reading is the same. When you shift weight from side to side, the reading shouldn’t change. Keep in mind that many home scales are not highly accurate (that is, they may not give your true weight, as a doctor's scale does), but consistency is more important for tracking changes.
How often should you weigh yourself? Once a week is usually enough, but that’s a personal choice. Some people get discouraged by fluctuations that occur over the course of a day or several days. If you do weigh yourself daily, take an average over the week. Weigh yourself on the same scale, at the same time of day (a good time is when you wake up), with the same (or no) clothes. Focus on changes over time, rather than a single reading.
Also see Body Fat Scales: Step Right Up?