Krunch, the two rides you recommended are in two different parks. The Simpson's ride is in Universal Studios, and Harry Potter is in Islands of Adventure. If I had to choose between the two for a one day trip, I would choose Islands of Adventure. In addition to HP, Spiderman and Hulk are also awesome. You could get a two park pass, but with only 7 hours of time it wouldn't be worth it.
The OP didn't say when they were going, but if it's during Christmas or Spring breaks, expect HUGE crowds and long waits. You can purchase front of the line passes for a hefty extra fee though.