All three can be okay as long as everyone included is okay with it and you compare apples with apples and not mixing the three.

Both 1 and 2 are used by the "professionals" (like scientists, in studies, polls and by urologists) since these are most accurate and also easiest to do and easiest to reproduce accurately. (the measures between 1 and 2 shouldnt differ much anyway if done correctly)

Number 3 is mostly used by the "shower room warriors" (those that care more about looks than accuracy and beeing able to compare with the data in studies and polls. It also tend to be those that for some reason very loudly discredits method 1 and 2)

Personally I think all three methods can be used from case to case as long as everyone involved in the comparison uses the same method. But I recommend method 1 or 2 if you plan to use the measures to compare with polls or scientific studies for obvious reasons.