Are you butchering any now? What criteria do you use to determine when to butcher them? If all you want is a little more meat on them when you butcher, do the same thing so you get a good comparison.
Like Molpet said, we all have different goals. In addition to his list, some people butcher when or before they start to crow or start to mate with the pullets or maybe hens. Or other reasons. You seed that "best" all over this forum. When you see someone say "best", they are saying what is best for them. That doesn't mean it's best for you.
One of my suggestions is to do some trial and error. Butcher some at different ages. With your chickens raised the way you raise them see what works best for you.
