For chicken, I'm generally doing more of a broth because I generally use a whole chicken. I can get chicken backs in bulk, but I'd have to buy a 40 pound box, and that'd make a whole lot of chicken stock.
For beef I use mostly shank and neck bones, though the shank bones generally do have some meat on them, which I pull off, marinate in barbecue sauce and serve on a bun like pulled pork.
The point to a bone-based stock (some chefs call it a bone broth) is to extract the collagen from the bones, making it thick when it cools. (I will sometimes throw some chicken feet into chicken broth to help thicken it.) You can get a second or even a third 'wetting' from good quality shank bones. I mix them all together.
Aspic, which is almost unknown in modern restaurants, and consomme, which is only slightly better known, take beef stock to its extreme limits.
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