most accurate would probably be an MRI, though you'd have to sell your body about 250000 times to afford it
Callipers are good to follow subcutaneous fat, but not for visceral fat, which a lot of men have trouble with and which is also the most "dangeoraus" fat.
IMO BF is pointless. what counts is knowing what way you are going, to do that, callipers + waist measurement is a good tool to use.
I'm sure Chillen will come in and post a couple of pages about dexa scans pretty soon, but I've seen some pretty conflicting stuff about the accuracy of the dexa.