THere is probably some subtle differences between the types of rubber being used. Some balls seem to use a very flexable rubber that seems to deform more when you put weight on it and looks like it would puncture more easily. Still I really don't think it matters that much, just make sure you put enough air in that you can sit on the ball and your knees make a right angle. Also avoid cutting brake and shifter cables into small pieces nearby. Those dratted little pieces of wire have popped two of my stability balls.
