The thing that is nice at Universal is the crowds weren't anywhere near Disney crowds when we were there.
At Seuss Landing my 4-year-old could have spent the whole day... and he did spend about half the day. The nice thing is he could ride the rides he wantd to again and again. At Disney we only rode Pooh once, because nobody wanted to stand in line for 40 minutes. At IOA, he rode Cat in the Hat 12 times!!!!
He also liked the play areas which again were not crowded, like the Jurassic Park one and the Olive Oil. He did not want to ride many/any rides which he thought looked scary - like River Adventure, Spiderman, Popeye, Ripshaw Falls etc, but baby swap worked great.
At Universal the kids could have spent hours at Curious George. They also loved ET and Men in Black.
LOTS to do at Universal.
We also did Disney last year and came back. This year we did both Universal and a bit of Disney and I really liked the pace at Universal but Disney (especialy MK) is Disney and there is a feel of magic in the air there for kids and adults. I just can't see returning to Orlando and NOT going to Disney.