Regarding the HC versus Asst. Coach question, that is more relevant for the D3's versus D2 and D1. It is definitely a plus to be seen by the D3 HC at one of the events, while the other division HCs tend to lean more on the RCs anyway, so you can gain interest from the HC if the RC likes you. And as others have said, the HF showcase is designed much better for having opportunities to actually talk to the coaches. It is a big plus that HF focuses on getting the coaches and players around each other a lot in the dugouts, on the field. So talking to an Asst Coach is better than not talking to a HC at Showball.
My 2017's experience with Showball is that the coaches tended to hang with each other and not mingle with players nearly as much. And the games were on scattered fields in different locations so it was random luck if a coach/school was at your game. HF had it arranged where coaches rotated fields so there was at least one game where they would be at an interested player's game.
So, as to HF vs. Showball, what do you think if his summer ball schedule only allows for the July 15-16 showcases. That weekend has all 8 Ivy HCs at SB (two coaches from some schools). Seems that leaves HF as second fiddle during that time.
If we can only do that time period, wouldn't it be best to do the Showball since most HCs will be there, even if HF's format is preferable?