Universal Studios, hands down! Not even a close contest.
The thing about DHS, is the layout is like a messy room. There's no flow from one "theme" to the next. Things are just plopped down wherever. Additionally, pretty much everything there is either a scaled back version of what it used to be, or it's old and run down, or it's new but relatively boring (LMA being a great example of this). In all honesty, DHS is at the bottom of the totem pole of all the Universal/Disney parks combined. If I've got limited time in Orlando to see both resorts, and I have to cut out a visit to one of the parks, DHS is ALWAYS the park that gets cut from the itinerary. On my last two visits to Orlando, I didn't even visit DHS once. The one thing that park has going for it is that it has the second best theme park attraction in all of Orlando... Tower of Terror (Spiderman is the best IMO). If you removed Tower of Terror from DHS, there would be no reason to ever bother visiting.
USF, on the other hand, is very well laid out. There is a logical and smooth transition from one section to the next (a great example of this is how they transition seamlessly from New York to San Francisco to Amity Island...brilliantly done). Another thing I love about USF is that there are sections that are there just for ambience and nothing else. In particular, in the NY section there are little nooks and alleyways to explore. In the Hollywood section, there are entire structures that are just there to add atmosphere and to make you feel as though you're really there. I have no doubt that if Disney owned this park, those areas would immediately be converted to souvenir stands and DVC booths. Also, the attractions at USF are far superior to those at DHS (except Tower of Terror).