That is kind of hard to answer. With hatchery birds it is hard to tell what you will get. That's what I've used with one exception and I've been generally pleased with them from both meat and egg production. I have gotten small ones but some nice sized ones too. You’d be surprised at how fast you can improve the overall quality of your flock in relation to getting larger roosters in just a few generations by carefully selecting your breeders. Don’t be afraid to start with hatchery birds. Unless you get lucky and tie up with a breeder that both knows what they are doing and is breeding toward your goals, you are probably not any worse off starting with hatchery birds.
I did get some designer birds from a breeder once and have been less than pleased with their size and productivity but I knew what I was buying. They are pretty and I wanted certain color and pattern genes. From that breeder I was comfortable I would get the genes I wanted. I figure I’ll be back to the size and productivity I want in a very few generations.
Hatchery birds often don't follow the breed conformation characteristics all that well. It depends on the person picking the breeding birds, that person’s goals and abilities. The Delaware and New Hampshire were developed as meat birds before the broilers were developed, but hatcheries I am familiar with don't breed for those meat bird traits so their birds don't have them. They are still not bad choices.
You might try contacting Kathyinmo if you want New Hampshires. I haven’t done it but the consensus on this forum is that she has some really nice ones. I’m not sure how fast hers grow but I believe her to be honest and that you will get straight answers to your questions.
What I suggest is to get a light colored bird, buff or white. The reason is that when you pluck some pin feathers are left behind. With dark-feathered birds you can see them so the carcass is a lot less attractive. With the light colored birds, those pin feathers are still there but you can’t see them. This becomes really important if you process a bird that is molting. It's not just the color of all those small feathers coming in but the pockets of dark dye under the skin. I did that three days ago with an old black hen that was molting. What a mess!
When selecting which specific rooster, first choose any genetic traits that are important to you and eat the rest. I don't know if you have any colors, patterns, comb type, whatever that are important to you.
Look for the fast growers. These usually turn out to be your biggest roosters anyway but you want one that has a decent feed to pounds of meat conversion rate.
Eat the smaller and breed the larger. You don't have to keep the absolute largest but don't keep a runt.
Look for general conformation. You'll get better at this with practice. Some roosters have more breast meat, some better thighs and drumsticks.
I try to pay attention to the rank of the rooster. I want one that is close to the top of the rooster dominance tree. It does not have to be the most dominant one, though that may be a good choice, but I want one with enough self-confidence that it can manage the flock without having insecurity issues. I find these to make better flock masters than the ones that they are all picking on.
Anyway, this is my take on it. Welcome to the adventure.
