For me? I'm not a huge Cars fan. I like Harry Potter a lot, but to be honest, I'm not a fan of digital/ 3D rides. I prefer AA's, physical props, and actually traveling through things. As cool as Star Tours is, I still prefer the Haunted Mansion, Space Mountain, Splash Mountain, etc.
So I'm actually more excited for the shops and little details of the Wizarding World than the actual attractions. However, I like the direction that both companies are going by building a whole land based on something. But since I'm an AP holder for Disney, I'd go to Carsland so I can visit the rest of the Resort. Universal Hollywood can be done in one day... heck, less than a full day.