Hi Vanessa. Not knowing what drills/exercises you will be using with your boot campers, I would say that it’s probably best to have a variety of weights since not all campers will have the same amount of strength. Medicine balls are great for power drills and so it’s best not to get too heavy since the whole concept of power exercise is speed.
Although you didn’t ask about this I’d just like to say that I’ve used medicine balls for several years with my clients, and love the ones that bounce (gives you much more flexibility of use). Have fun!!!