If a crock pot recipe offers both options, is it better to cook using high or low setting?

The longer chicken broth cooks the more it will boil down and the tastier it gets. The flavors have more time to mingle. However, 4 hours is a good amount of time. As a suggestion use scrap chicken to cook. Then, so the meat will not be chewy, discard the chicken and put in fresh sauteed chicken cutlets diced toward the end.