Hi OP: Congrats on experiencing the most amazing ride/immersive areas of any theme park
As to which side takes more time to tour, it is individual. However, we always spend a lot of time on the studios side, especially the shops in Diagon Alley, the Gringotts ride (amazing), eating at the restaurant, and wandering Knockturn alley. To us, this side has more that we want to do and see. However, the IOA side is fantastic too with Ollivander's wand shop and FJ.
We spend most of our Universal time in the HP areas.
Don't forget to knock on the door at #13 Grimmauld place, and Kreacher will peak out the upstairs window