I bought my 15lbs digital fish scale at Academy's Sporting goods. I don't even remember what brand it was. Can't tell you which ones are better either, since I have only bought one. I just remember looking at all of them and picked one with the best "claimed" accuracy and still at a reasonable price. In any case, the best of the 15lbs ones will be accurate to ~2-3 Oz, which is plenty good enough for weighing planes and calculating wing loading.

I don't know what my bathroom scale full-scales at, probably 250 or 300lbs if I have to guess. I would be be mighty impressed if it's 1% accurate, at best. This means I'll have a margin of error of 2-3 lbs, not too good for weight planes between 5-15lbs.

Plus, like I've posted here before, I recalibrated my bathroom scale to read 5lbs less whenever my wife stands on it, so it's all off anyways.