Right now they're pretty much tied for me. When I look at it theming wise I pick IOA hands down(even though Diagon is in a league of its own). Ride wise, USF is so strong with Transformers, MIB, Mummy, and now Gringotts all as must dos, but IOA is slightly higher, with Forbidden Journey, Spider-Man, Jurassic Park, Dudley, Popeye, Hulk, and soon Kong. Show wise, USF wins that match easily...with Animal Actors, Horror Makeup Show, Terminator, and Shrek, it's no contest.
I think right now they're even, but come next year it'll be IOA...and after the Kidzone redo it'll probably swing back to USF.
Just shows how good both Uni parks are!