Medicine/swiss ball selection for tuff cuff

Im thinking about buying tuff cuff for my strength and conditioning guide but i dont know which kind of med/swiss ball to buy. Should i buy a big bouncy one or a 12-pound small one or idk just please let me know what you use or steven ellis it would be great if you could tell me!!

5 kg bouncy ball. But it may be too heavy for you to start out with, so go with the 4 kg. Med balls can be expensive if you order them from a physical therapy store or sports store. Try Wal-Mart first. PerformBetter.com makes the best med balls imho.