Start with 10% of your body weight.
It's the sweet spot where your body is being challenged enough to adapt without overloading your joints or burning you out in week one.
Here's exactly where that puts you:
150 lbs → start with the 12 or 16 lb
180 lbs → start with the 20 lb
200 lbs and up, or already training regularly → start with the 20 or 30 lb