DEXA body scan but its expensive and you won't be able to test it daily or weekly realistically.
water tank would be next but it also costs and it may not account for stuff like bone density.
bf% calipers you hold are within a radius of your bf, but you would need to test a lot over a period of time to get an accurate range of where your bf is.
and finally posting up a few pics of yourself on a board like this will give you an idea of where you might be perhaps just as accurate as anything out there. bro's on here are good at analyzing your bf based on pics