Body Fat Estimation

hi guys,

can someone point me in the right direction for some article or previous forum discussion on methods of body fat % calc?

a hand held bio impedance says im 20.7%,

online calculators based on neck and waist seem to average me at 14% ( i tried 10 different sites).

and calipers done by a non expert said im 12.5%

so id like an article, discussion or explanation of the pros and cons of each, and what can be seen as the most accurate?

thanks!