The standard cornish will breed true. The cornish cross won't so you have to buy chicks each time. Alot of people do that and it works well, you buy a batch of chicks , grow them out and freezer them and you are done with chickens until you need another batch. When we raised the cross they just didn't have the taste that a heritage bird has.
From the birds we raise each has a quality
Buff Orpingtons have huge leg 1/4's - we are growing out some Light Sussex this year and it looks like they are going to be the same way
Rhode Islands, Marans and Java's have a long wide breast - because of the body shape
Speckled Sussex were bred as a meat bird and have more compact thicker bodies
Dark Cornish are solid, meaty. Even as chicks when you pick them up they weigh more than others.
Steve