Hi,
WDW is great, lots of fun. So is Universal, different feel, less "cutesy" . We prefer Universal these days, partially because of the on site hotels. It's very relaxing to go back and forth on the water taxi's to the Portofino, and we enjoy the quietness of the hotel after a day at the parks. The other on site hotel is a little more "happening" and you can walk to Universal from that location.
We took my kids, ages 5 + 10 at that time, to Universal and IOA , 2 years ago. They both had a ball!!
I would suggest you order the free video from Universal. It's not really very informative but it shows many of the rides and really gets you in the mood! You can order it on-line or you can call 1-800-UESCAPE.
Everyone is happy to answer your questions!