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.