There are a few different products and methods for measuring body composition (I’m not sure if you are asking for a comparison within different products to use, or within the same products to know which brands are better).
You can use skin fold calipers (take a little more training, but tend to be more on the accurate side depending on the testing skills of the trainer), hand-held bio electrical impedance machines (easy to use), body circumference via a tape measure (easy to use), and hydrostatic weighing in water (one of the most accurate measures). There is also a newer method for analyzing body composition using a DEXA scan that is supposed to be very accurate as well.
As long as you are using the same product to take retests, you can get a basic picture of body composition trends.
I hope I’ve helped to answer your question.