I went as a spectator to WIHS a few years in a row and would DEFINITELY go back! Haven't seen/been to the others to compare, but WIHS was fun.... and so easy for us to just take the metro into the city.
I would want to go watch the Syracuse Invitational for the porthorse cup and the Maclay
That show is no longer around and the Maclay is in KY now.
I was disappointed in WIHS, have never been to Harrisburg or the Royal, but I would rather go to one of them. I wouldn't even consider the National Horse show anymore, its nothing but another show IMO, nothing special anymore.