"The body mass index has long been criticized as a flawed indicator of health. A replacement has been gaining support: the body roundness index." Article unfortunately doesn't give the freaking formula for chrissakes; it's "364.2 − 365.5 × √(1 − [waist circumference in centimeters / 2π]2 / [0.5 × height in centimeters]2), according to the formula developed by Thomas et al.10"
BMI is the best measure we have for statistical purposes (i.e., a population) because it's been around for 50(?) years and is what is often used in studies, so you can compare one study to another using BMI.
It's also not terrible for a population because it averages out. But for an individual it is definitely not a good measure because there are way too many other variables that matter.
For individuals the tg/HDL ratio is promising as a great marker for insulin resistance (lower is better). But it requires a blood test, for academic purposes it's also good because most checkup blood tests have these two markers recorded.