It'd be a tough call but I think I'd go with Universal Studios. Feel liek there is more that I could reride throughout the day and walk around to see. I love Simpsons so could hang out in that area for a bit, but the ride woudl be a one or two time thing, and Diagon Alley has a lot to see and I coudl reride Gringotts a lot. Mummy, RRR, MiB, and Transformers I coudl reride all day. Plus got the toher rides and shows.
In IoA the only things I could really reride a lot would be Kong and Spider-Man. I love Hul, FJ, and DC but give me a big heaache/nausea if i reride them much so woudl have to spread them all out a lot. Hogsmeade is good to walk around but not as much to see as DA. I could reride Dudley and Bluto a bit but would only really want to do them during the one period so I was jsut getting wet the one time.
Once Fast and Furious and Nintendo Land especially (if it does go into US) then it woudl be hands down US.