I use the scale, but I don't think they are that accurate, at least at higher body fat percentages. I would test my BF at night and get at times as much as 7% difference. One night I checked once, then went and watched a movie, eating nothing and just drinking water. I checked after the movie and found I'd lost 2 pounds but gained 1% BF according to the scale:P

I like the mybodycomp because it takes into effect so many different measurements instead of just hip to waist.

The only way to test for sure would be one of those water tests and that would be expencive. Just pick a method you like and stick to it. Look for drops in the number more then the number.