Yes the most accurate is DEXA and hydrostatic. Second, to that are calipers. Remember, unless you are training an athlete, that for some reason needs absolute BF, then, whatever you use as long as it is consistently performed by the same person, with the same method, will be valid and accurate in terms of showing change.
I use Lange calipers and the syndex card. This is so easy. The card does all the calculating and I just measure three sites per Jackson/Pollock. I have been off about 1.5% from hydrostatic, expected differences can be up to a 3% error factor.
Creative Health Products carried both.
Hydrostatic weighing is the standard (didn’t know about DEXA, thanks for that one) but I’ve only seen it used in the clinical setting. I have used calipers since 2002 and have very good consistency now but that took time. If your really looking to dial in the results you may have to go with more elaborate (hydrostatic and DEXA) methods. Its not cheap so be sure its necessary. Personally, 7 site calculations have given me the most consistent results and it also allows a good image of the clients body fat distribution. I use this distribution to assist in obese related cases, to detail possible underlying issues.
nothing is going to be absolutely accurate and with any calipers (and I like the Skyndex that was mentioned) it is dependent on your experience and consistency doing it. DEXA is good because you can get bone density as well, Hydrostatic weighing has been and still is the gold standart, bodpod is pretty accurate but might be hard to find one.
Nothing wrong with a tape measure and watching the inches get smaller. I have learned through experience that body fat % is less important that losing inches and for obese clients can be a negative experience.