Back before the advent of the Cornish X, around the 1950’s, two breeds had been developed to be commercial meat birds, Delaware and New Hampshire. In addition, some flocks of White Rocks had been developed to be used as meat birds, but some were bred to be more dual purpose. But that was a long time ago. When the Cornish X came along, people stopped breeding these birds for meat and they degenerated to be pretty equivalent to other dual purpose breeds, at least in the hatcheries. If you don’t breed for a certain trait in chickens, such as the traits that make a good meat bird, the flock loses those traits. Each hatchery has a different person deciding which chickens get to breed and they all use different criteria so there are differences between hatcheries. I haven’t sampled all the different breeds from all the different hatcheries, but I have a few. I can see some differences between the same breed from different hatcheries but in general, from a meat bird standard, I don’t see a lot of differences between dual purpose breeds. If you knew what hatchery certain birds come from that someone likes then you can get a much better idea of what the birds from that hatchery are like. But without knowing which hatchery it’s just a crap shoot on what you get to a large extent.
There is even a wider discrepancy between breeders. Some breeders are breeding to the SOP for what the judge sees so they can win ribbons. These birds are going to be bigger than hatchery birds because the SOP calls for big birds. He bigger the adult bird the more they eat so it costs more to feed them. Being big may be more important for a show bird than a hatchery bird. A few breeders look more at production traits than the traits the judge looks for. They may not win any ribbons but if you are going to eat them, what difference does it make? There are a very few that may breed for both show qualities and production qualities the breed is supposed to have. That’s why you see statements about certain heritage breeds being endangered although you can get all kinds of them from hatcheries and a lot of people breed them for show. To the purists, a true heritage breed combines show, production, and behavioral qualities. That’s hard to do. Then you go to the other extreme. Some people that don’t understand the SOP just take hatchery chickens and breed them without knowing what traits they are going for. These can be worse than hatchery chickens. The only advice I can offer on breeders is to talk to them and see if you can determine if they know what they are doing and what traits they are breeding for. It can be a minefield but if you find a breeder that is breeding for what you want it can be a blessing.
The traits that make a chicken a good meat bird might vary from person to person. Different breeds have different conformations so you can get different ratios of white meat to dark. That’s where the Dark Cornish come in, they add breast meat. Whether you confine them and feed them everything they eat or whether you depend on pasture can make a difference. Do you want to butcher them all at the same time like you do with the Cornish X or are you like me? I have limited freezer space so I need a bird that can support itself some by foraging and wait until I have room in the freezer to butcher. There are only two of us so I don’t need a huge bird to make two meals. I can make two good meals for us with a pullet, I don’t have to have a cockerel. With a large family you might need a bigger bird. Since half the chicks I hatch are pullets, half the chickens I butcher are female. If you only want to raise males then being able to sex them at hatch would be a big plus. That means make red or black sex links. If you fry them or grill them you need a bird that you can butcher at a younger age. I’m quite happy to bake or stew them so I can handle an older bird. Some chickens put on meat at a fairly young age while others are mostly bones until they mature like Brahma or Jersey Giants. At what stage of maturity you butcher them can make a difference. Some people pluck their birds, some skin. If you pluck, a dark-feathered bird will leave behind a lot of noticeable pin feathers. The light feathered birds still leave pin feathers but you don’t see them so the carcass is prettier. If you skin it doesn’t matter. When someone tells you that a certain cross makes a wonderful meat bird, I’m sure it does for them and it might for you.
The only chicks I’ve gotten from the original early to mid 1900’s meat breeds of Delaware, New Hampshire, and White Rocks were Delaware’s from Cackle. The Delaware cockerels made a nice meat bird for me but the Black Australorp were just as good, though when I plucked I had a lot more black pin feathers to deal with. Those Delaware cockerels were not that much like the original meat birds in how fast they packed on the meat but they were not all bones when I butchered them around 16 to 20 weeks. The 20 week olds had a lot more meat, but so did the BA’s.
I suggest you decide what traits you think will make a good meat bird for you and start from there. The quality of stock you start with will make a difference with your results. How to determine the quality of your starting stock is what I don’t have a good answer for you, other than either take your chances with a hatchery or try to find a breeder that suits you.