I would have to agree with breeder birds over hatchery, size, egg laying, etc. And Tim is correct on the size of the store bought birds and getting spoiled. There are a bunch of Perdue chicken houses around our area and i'm here to tell you those birds are HUGE with a capital HUGE. There is still much room for improvement in any poultry, it takes time and set goal in mind. If you want meat then you are looking at putting a number on each chick, weighing each of them as they grow out and only keeping the fastest weight gain and heaviest birds as breeders. And even then you are only going to get so much out of them, you'll never make a heritage bird that can compete with a cross. But you can increase the size over time.
Steve
Steve