My experience is that it's less about the breed and more about the hatchery. Each hatchery (or chicken raiser or whatever) tends to have their own genetics for a given breed - hence Breed X from one hatchery may do better than Breed Y, whereas at a different hatchery, Breed Y will do better than...
I believe they're 20-21 weeks. Some have started laying - found an egg in the box when I got home with them last night. Another showed up around noon today. They're Gold Comets.
I just purchased some pullets and got them home to discover they had been debeaked. Thankfully, it's not very severe (only the upper, and maybe 1/2 the way between the end and the nairs). Also, I discovered they had been eating crumbles. This being my first time, and not being able to forsee...