Scales

In short, I just want to know what the best, most accurate and affordable scale out there is.

My friend and I have the Weight Watchers scale from Costco and have both had the same bad experience. I've been using my scale on my tiled bathroom floor. I would weigh myself and get one weight, then a few minutes later, I would weight myself and get a completely different weight, off by a pound or two. In between weigh-ins, I would not do anything that would make me gain or lose weight, like eat, drink water, pee or poo. My friend has had the same experience. He uses his on the hardwood floor. We have tried changing the batteries, and even used a level to see if the floor is level.

Any suggestions?