Getting in Shape

Almost any of them will do an okay job. Basically this kind of body fat is using Bioelectrical Impedance to determine body fat, and none of them are terribly accurate. That said, what it will give you is a good baseline for where your starting point is and it will give you a good idea of what progress you've made. If you can test them before you buy them, step on and off of the machine 3-5 times, allowing it to calculate & recalculate your body fat each time. if there's a large discrepancy between readings, then you may want to look into a different brand.

In addition to buying a body fat calculating scale, I would also make an appointment at a local university or at a health center to get tested using a different form of measurement as well (skin-fold testing, DEXA, hydrostatic weighing, etc.), that way you'll have several fairly accurate readings that you can test against along the way.