Based upon my, and also my son's, experience we ranked PTW's a runaway first, with HeadFirst second, and Showball a fairly close third. All three really favor pitchers (my son is a 2-way player), but PTW's setup of NOT starting with a 1-1 count both gives the hitter a better opportunity to hit, while also making it more realistic for the pitcher. PTW also has all of the players on just one field, so all of the coaches can see each player. The Showball academic coaches camp also had their simulated games on just one field, while Headfirst had 4 games going on at once.
PTW also had players fielding their positions during BP, which gave them addtional opportunity to display their defense above and beyond the typical 4 to 6 balls hit to each player during the normal defensive segment of the showcase. And PTW used laser timing on their 60's, eliminating the potential inaccuracies of hand-timing.
With all three, the coaches were, naturally, most interested in rising seniors. The fact that PTW had a much smaller number of players than HeadFirst or Showball at the three different PTW events my son attended made it easier for him to attract attention.
That being said, I think all 3 are probably worthwhile experiences for rising juniors, allowing them to be seen by coaches. Of course, the best route is to attract interest during these events as a rising junior, then target the camps of the individual schools in which there is mutual interest prior to your senior year.