Thought I'd throw in my two cents
Me and my family don't get to visit Disney often, but ever since I was a child, I've watched the films, listened to the music and that's why I love Disney so much. The nostalgia factor is powerful. I well up whenever I find out I'm heading to Disney for a holiday!
That said, I also really enjoy thrill rides. Rip Ride Rockit was so much fun when I first experienced it
That's why I like both parks, for different reasons. They have different target groups, and that means it's difficult to compare them.
As much as I love Harry Potter, I much preferred the walk through of the castle to the ride. I thought the ride itself was too loud, and I freaked out over the spiders and just kept my eyes closed :/ So I can't really give a thorough review of the ride, I only went on it once and didn't even see the dementor part! :lookaroun
So Universal= thrills. Disney= theming and atmosphere. I guess that's a pretty simple summarisation.