sebutler, CTX is thought to have less in-person variability and is preferred over NTX. https://news.mayocliniclabs.com/2023/08/07/laboratory-testing-of-bone-turnover-markers/
I think because of flow and dilution. Blood being of more consistent volume.
I have read that NTX is less susceptible than CTX to variations caused by circadian rhythm and food intake.
I'm curious about how you arrived at the thoughts about which would be better.