As a loooooooooong time Disney addict, I had managed to make it to Orlando quite a few times without ever setting foot on Universal property.
Last spring we stayed for a few nights at FWilderness, and decided to only do the universal parks. I was skeptical, though I figured that we would have fun.
I was completely and totally blown away by the parks.
My family liked US, and really enjoyed the park. Lots of attractions with a completely different "feel" than Disney. It really is all about the movies and entertainment, and keeps to its theme extremely well. Disney/MGM is teriffic too, but seems to be struggling to keep to its them.
We really loved Universal. It compares favorable with much of what Disney has to offer in many ways!
IOA, however, is the best Theme Park that I have ever seen. Hands down, flat out, the best.
The ONLY real thing that we felt was missing was a night time "closing spectacular" like Fantasmic or Reflections of Earth.
Leaving after one of those is an incredible high. If Universal ever gets that part right, watch out mouse! Until then we will be happy to visit both!