The bouncing balls allow you to do tosses against a solid wall or pavement. Tennis players can stimulate their muscles while simulating their game by hurling a bouncing medicine ball across the net. The non-bounce ball is used by many advanced athletes because it is softer on the hands to catch and doesn't roll away when it lands. This is an advantage in outdoor squat throws where you hurl the ball high in the air but don't want to continually chase it. The same goes for indoor group exercises in which a non-bounce ball is easier to manage in crowds where there are multiple balls and multiple users.
Most people prefer the new rubber balls over more authentic leather ones.
The recommended weight of a medicine ball depends on your age, sex, size and purpose. An 8-15 lb ball is a good weight for an abdominal core workout. A 4-10 lb ball is good for tossing exercises. Use a heavier ball, 15-30 lbs, for leg exercises that build hamstrings and quads. Women and juniors usually use balls on the lower end of the range, while men typically use balls on the higher end of the range.