Showball is almost a poor man's Headfirst if I recall. Just make sure their are schools at the event that fit your son's profile. You will find a greater percentage of assistant coaches from schools at Showball and more Head Coaches of schools at Headfirst.
However, you will get exposure and the same premise of two scrimmage games and pitchers will get two appearances over two games.
If you have to make a choice, I would go with Headfirst but make sure the schools listed work in your son's academic range. If you have the resources to do both, it can be worth it.