They are both random and arbitrary. Using the human body as a standard is probably useful for medical purposes… using water as a standard is probably useful for other purposes…

Considering temperature itself is dependent on other variables like atmosphere, any temerature system is going to be random and arbitrary…

Kelvin at least has a theoretical bottom for the coldest something can get maybe? But still, Kelvin is also arbitrary because it uses Celsius as a standard, which is random and arbitrary…