Well, guys, I hate to break it to you, but IOA has only opened but 2 major attractions (one that it shares with USF) and a few minor attractions throughout it's entire 16 years of existence.
USF is a much more compelling park to choose if I only had one day to do Uni. Say they were a Potter fan. I'd start in USF, like any proper wizard should - in Diagon Alley. Grab a wand, experience the land for awhile and then board the hogwarts express over to Hogsmeade. Grab a Butterbeer, go wait in line for Forbidden Journey, then eat at Three Broomsticks. Take HE back over once i'm done and experience the rest of USF.
That's how I would do it as a huge Potter fan, but as just a regular Joe Schome, where is that person gonna go? Where the newest addition is of course? So to Diagon it is! There's honestly nothing drawing guests to IOA right now immediately, especially now that you can get there via Hogwarts Express.