There are so many body composition products on the market, are you looking for something practical or more a product that has the least amount of error as possible?
If looking for the “gold standard”, it is my understanding that DEXA which stands for dual energy x-ray absorptiometry is the gold standard and gives you bone mineral density readings also. Is it practical, not really unfortunately. Depending where you live, you can bet at the minimum price it will cost $100. There are other tools such as Bod Pod and the dunking tanks.
Something more practical is using calipers if you get really good at them, using BIA but understanding the variables that affect readings, and being consistent with measurements in my opinion. I’m a big fan of the “how my clothes fit” method especially if the client does not want to be measured or does not want to pay for such things.